INTRODUCTION

The geological history of the Pliocene to Quaternary Indo-Pacific coral reefs is relatively well documented worldwide (Montaggioni & Braithwaite 2009; Montaggioni et al. 2023). Coral and molluscan assemblages have been particularly well studied in the various reef biozones from outer reef slopes to backreef zones. Changes in sea level in relation to the successive glacial and interglacial periods over the past 2.6 million years have resulted into significant changes in faunal assemblages (Harland et al. 1989; Paulay 1990; Lisiecki & Raymo 2005). Comparison of Pleistocene coral and malacological faunas with their Holocene and modern counterparts reveals that species extinctions have occurred in numerous Indo-Pacific reef sites on both global and regional to local scales. There is an abundant literature devoted to corals: Paulay & Spencer (1988) on Henderson Pitcairn islands group, Chevalier (1979) on French Polynesia, Stoddart (1973) and Potts (1984, 1985) worldwide, McManus (1985) on Southeast Asia, and to molluscs as well: Ostergaard (1928) on Oahu Hawaii, Ladd (1966, 1972, 1977, 1982) on West Pacific Islands, Hayasaka & Oki (1971) on Kagoshima Japan, Taylor (1978) on Aldabra (Indian Ocean), Crame (1986) on Kenya, and Paulay (1990) on tropical oceanic islands.

In 2008, Ludwig Blanc brought to one of the authors (JL) three specimens of an unidentified Strombus species collected from a marshy area just extracted by sub-surface dredging on the lagoon margin of Niau Atoll. In 2008 and 2010 a rich assemblage of fossil molluscs was collected at the same site (JL). This gave rise to the description of three new gastropod species (Strombus ‌blanci ‌Tröndlé & Salvat, 2010, Terebra ‌niauensis ‌Tröndlé & Letourneux, 2011 and Turbo ‌fakaauensis ‌Tröndlé & Letourneux, 2012) and to a comprehensive study of the 120 listed species (Salvat et al. 2018). This predominantly lagoonal assemblage was reported previously as dating from the last interglacial stage (128 000-116 000 years BP), with identifications of endemic species and species extinct since that time in French Polynesia, but it was later dated from the Plio-Pleistocene (Late ‌Pliocene-Early Pleistocene) by Montaggioni et al. (2023). Moreover, in September-October 2022, we (BS) carried out on more recent lagoonal mollusc assemblages in order to obtain datations on Holocene material.

The objectives of the present paper are: 1. To identify and describe the molluscan new species and assemblages from both the reef rim and the lagoon in relation with the local stratigraphical history. 2. To reconstruct the evolutionary stages of molluscan development from the Late ‌Pliocene (i.e. the last 4 million years) to the Holocene including speciation and extinction events.

ENVIRONMENTAL SETTINGS

Geography

Niau, also known as Fakaau, is a small, almost circular atoll in the Tuamotu archipelago in French Polynesia, located at 16°10’ south latitude and 146°20’ west longitude (Figs 1; 2A). Niau atoll is less than 50 km west of Fakarava, one of the largest atolls of the Tuamotu and located 350 km southwest of Tahiti. Niau is a closed atoll with a continuous emerged subcircular reef-rim, the width of which varies from 0.5 km in the northwest to 3.6 km in the southeast. The reef-rim completely isolates the lagoon waters from the open ocean. The total surface area of the atoll, bounded seawards by an outer reef-flat zone, is around 60 km2. The emerged part, covered with vegetation, is 22.15 km2 and its central lagoon 31.88 km2. The atoll perimeter reaches 30 km (Andrefouet & Chauvin 2005; Butaud 2006).

Ocean margin

Niau Atoll is bordered by a fringing reef, 100 to 200 m wide (Fig. 2B) presenting the usual biozonation observed throughout the Tuamotu archipelago, from the ocean inwards: a reef front, usually, in the form of an algal crest where the ocean waves are breaking, a reef-flat zone a few decimeters deep at mean tide level, a conglomeratic platform (“old reef conglomerate”) and a sandy beach. Along the north-western and north-eastern edges, another fossil reef unit crops out between the modern reef flat and the coconut grove. In the northwest (Ofare) and northeast (Tupana) sectors (Figs 1; 3A) this unit occurs at the upper limit of the beach, with a micro-cliff 1 to 3 m high. This palaeo-reef had been spotted by Veeh (1966), but the collected and uranium/thorium (U/Th) dated coral specimens were not accurately field positioned. However, the dated reef outcrops are postulated to be those found at Ofare or south Ofare where they are very accessible. Veeh (1966) obtained ages ranging between 120 000 and 160 000 years BP. In the southern part of the atoll, the reef-flat zone facing the ocean is bounded seawards by an ancient Porolithon ‌Foslie, 1909 dominated algal ridge, the height of which exceeds locally 1 m (Fig. 3B). Due to the breaking wave effects, this ridge is broken up into about 1 m-long, a few centimeters thick fragments.

Uplifted atoll and “feo” reliefs as the elevated atoll reef-rims

Niau is a slightly raised island, as interpreted to have been elevated by relatively recent tectonic movements (McNutt & Menard 1978; Lambeck 1981; Montaggioni 1989; Montaggioni et al. 2023). Except for the extreme north of the atoll, in the area of the airstrip, characterized by steep cliffs about 8 m high (Fig. 4A), the average altitude of the reef-rim is 3 to 4 m. These elevations make Niau a so-called “uplifted” atoll, when compared to most Tuamotu atolls, the maximum height of their framework-built surfaces (i.e. reef flats) rarely exceed 0.5 m above present mean sea level. These surfaces were overlain by sandy deposits, during the last millennia, thus resulting in maximum atoll elevations averaging about 5 m. Reliefs of “feo” type (Butaud 2006; Cibois et al. 2007; Salvat et al. 2018), regarded as markers of uplift (McNutt & Menard 1978; Lambeck 1981; Montaggioni et al. 2023) occurred in Niau atoll as well as in six other nearby uplifted atolls (Makatea, Mataiva, Tikehau, Rangiroa, Kaukura, Anaa). Feo are jagged fossil coral reliefs of approximately 3 to 4 m in height (Fig. 4B, feo inland and Fig. 5A feo on beach, Niau Atoll). A dense forest, difficult to penetrate, has developed over these reliefs, locally separated by excavations, about 2 to 3 m deep and covered with plant debris. Some excavations between the karstic reliefs lead to caves. The limestone rocks, constituting the core of the feo, are intensively calcitized and dolomitized.

The coconut grove

These fossil reefs of feo type are bordered oceanwards and lagoonwards by a coconut grove, except in the airport sector to the north of the atoll, where the coast is made out of cliffs and devoid of fringing reef (Fig. 4A). These two coconut groves are nearly 8 km2 in area (Butaud 2020), which are three times smaller than the feo-built, raised rim zone.

The swamps

The marshes near the lagoon exhibit low-growing or man-high halophytic vegetation. They cover a total of 1.22 km2 (Butaud 2006). The swamp (Fig. 5B) is colonized by Cladium ‌mariscus (L.) Pohl, 1810 (Cyperaceae ‌Juss.) – “uuti” locally – and is found at the so-called “La Piscine” site (swimming pool), close to the ancient Ofare village that was used as an extraction area of materials for constructing the airplane runway in the early 2000. In the middle of this swamp, five dredging basins cover seven hectares. In the centre of swamps near Ofare and Aturona, there are archaeological sites which are currently under study: the Vaiohua platform (16°08’08.46”S, 146°23’09.48”W) and the marae from Aturona (16°08’26.53”S, 146°19’54.30”W). Another marshy area bordering the lagoon to the southwest also includes an archaeological site at Hivaroa marae (Fig. 1). At Ofare-Vaiohua (Fig. 1) in the Cladium ‌P. Browne, 1756 marshy area, there are patchy, calcareous crusts among the low-growing or shrubby vegetation cover (Fig. 5B, C). These crusts are flat-topped and uniform, but almost entirely covered by a terrigenous, organic-rich deposit, about 0.30-0.70 m thick. Closed to the dredging basins, south of the Vaiohua platform, are found sandy mounds bearing large, 0.30-0.10 m thick, fragments of this calcareous crust at top. This crust is known by pedologists in hydromorphic marshy soils as “limestone crust” (Jamet & Trichet 1987) and reported by Butaud (2006) from Niau Atoll.

This pedogenetic crust type, also called “caliche” or “calcrete” (Lidz 2011), is a paleosol formed from limestone source rocks. In some arid to semi-arid regions, these paleosols can reach several metres in thickness, but in humid tropical climates, rarely exceeds a few centimetres. Caliches are products of chemical alteration resulting from microbial mediation during rainy and dry seasons. During rainy periods, limestone rocks are dissolved and percolating waters enriched in calcium and carbonate ions migrates downwards to the water table. During drier periods, infiltrated waters tend to rise upwards to the ground surface by capillarity. There, waters are evaporating, thus allowing Ca2+ and CO32- ions to precipitate, thus generating a surficial crust.

The lagoon

The lagoon at Niau occupies the central part of the island, completely bordered by coconut groves and locally by marshy areas. The lagoon is called “vaitamae” by the natives, meaning “fermented, rotten, withered” water (Torrente 2018). Its surface area is approximately 22 km2; its depth averages 2 m. Small, deeper basins can reach 5 to 6 m depth. Due to lack of direct water exchange with the ocean, the lagoon is brackish and salinity does not exceed 32 g/l occasionally (Landret 1977; Lagouy pers. com. 2009). After heavy rains as in March 2010 (Galzin & Verducci pers. com.,) salinity was shown to vary between 23.1 and 23.6 g/l and temperature between 29.9°C and 31.8°C. Ocean water resurgences through the reef mass and karstic structures, locally called “marite”, explain such a salinity in the lagoon. These “marite” occasionally presenting bubbling waters are a few metres deeper than the bottom of the neighboring lagoon. Strong swells during cyclonic periods bring ocean waters into the lagoon, through overwashing of the emerged atoll rim in its lowest places. This was learned by Agassiz (1903) during the Albatross Expedition in 1899-1900: the atoll rim at Niau would have been overwashed during the 1878 cyclone. He noted that the lagoonal waters were very salty and at a temperature of 28°C. The “Pacific Island Pilot”, a navigation manual from 1920 and 1926, reported that before the 1878 cyclone, the lagoon was a kind of freshwater lake becoming brackish since this hazard event. However, this observation should be taken with caution. During the cyclones in 1983 (Orama in February; Veena in April) which destroyed the majority of buildings in Niau, it was reported to us by Ms. Torohia (resident at Tupana) that waves broke in Ofare and Tupana areas and overwashed the reef-rim to reach the lagoon. Note also that during usual, calm periods, intense evaporation of lagoonal waters is operating, thus increasing salinity. Therefore, one must consider that the lagoonal water regime typified by infiltration from the ocean through the karstified rim structure, precipitation, evaporation and occasional massive flooding during cyclonic events determines salinity values that can vary greatly over several decades.

The Niau lagoon is partly filled with “kopara” (or “opara” locally), consisting of cyanobacterial mats, coloured from red to green (Rougerie et al. 1997; Trichet & Delage 1999), up to 2-3 m in maximum thickness and found at depths of 4 to 6 m on the bottom (Galzin & Verducci pers. com.). Apart from the molluscan fauna, the lagoon contains three fish species only: 1) Chanos ‌chanos ‌(Forsskål, 1775) or milkfish, from the family Chanidae ‌Günther, 1868 (Galzin & Verducci pers. comm.); 2) Oreochromis ‌mossambicus ‌(Peters, 1852) or “tilapia” from the family Cichlidae ‌Bonaparte, 1835, introduced in the 1950s (Tröndlé & Salvat 2010); and 3) a small goby Bathygobius ‌cocosensis ‌(Bleeke, 1854). The first species, locally called as “pati”, is feeding on kopara and is an important local food resource (Torrente, 2018). We also note the presence of a shrimp, Palaemon ‌debilis ‌Dana, 1852 from the family Palaemonidae ‌Rafinesque, 1815. The molluscan fauna, currently living in the lagoon, was identified taken into account some recent species introductions.

AGE AND DEPOSITIONAL HISTORY OF THE EMERGED ATOLL RIM

Based on isotope dating (Montaggioni et al. 2023), the raised carbonate reliefs that make up the atoll rim are proven to belong to three distinct reef generations.

Plio-Pleistocene Feo Unit

The oldest, deeply calcitized feo, dated by using the strontium isotope method in several sectors are Late ‌Pliocene or Early Pleistocene in age: top of the Airport cliff (samples N49 and N51): 1.124 Ma (between 1.2 and 0.94 Ma) and 1.140 Ma (between 1.31 and 0.96 Ma); inner island airport sector (sample N100): 1.893 Ma (between 1.488 Ma and 2.105 Ma); Ecole (school, Fig. 1) sector in the north-north-east of the atoll (sample N98): 1.411 Ma (1.690 to 1.220 Ma); Pension sector to the east (sample N14): 1.328 Ma (between 1.200 to 1.485 Ma); Dragon sector to the south (sample N7, beach site; sample N87, inland site): 3.672 – 3.800 Ma – and 3.146 Ma; Tiramo sector to the southwest (sample N84): 1.092 Ma (see Montaggioni et al. 2023: supplementary material, table S5).

Two caliche samples (Fig. 5B, C) were dated using the strontium isotope method. Ages range from 2.245 Ma (sample N42) to 2.505 Ma (sample N44). This Early Pleistocene age relates to deposition of this reef unit as observed along the northern rim side. However, the Sr-derived ages could be biased, due to mixing between marine and fresh water Sr isotopes during caliche formation. This may result in apparent rejuvenation of caliche deposits.

In the Plio-Pleistocene feo zone some large valves of giant clam Tridacna ‌gigas ‌(Linnaeus, 1758) and Tridacna ‌squamosa ‌Lamarck, 1819 have been collected by natives. We noted also the presence of scattered specimen of large Codakia ‌punctata ‌(Linnaeus, 1758) with their two valved closed. Strontium isotope dating of a shell Tridacna ‌gigas sample (Niau TG) returned an age of 2.337 Ma (Early Pleistocene), consistent with the age of the internal feo zone.

Plio-Pleistocene age of molluscan and coral thanatocenosis

Based both on the available data on Niau geological history about fifteen years ago and on the apparently "fresh" nature of the molluscan shells collected at 4 m deep within loose sediments, Tröndlé & Salvat (2010) inferred an age of 120 000 years (Late ‌Pleistocene) for Striatostrombus ‌blanci ‌(Tröndlé & Salvat, 2010). This age was also attributed to the two other new species of molluscs extracted from the same lagoonal deposit (Oxymeris ‌niauensis ‌(Tröndlé & Letourneux, 2011) and Turbo ‌fakaauensis ‌Tröndlé & Letourneux, 2012). In 2013, the attempt to date three molluscan shells extracted from the thanatocenosis (Striatostrombus ‌Dekkers & S. J. Maxwell, 2018, Polinices Montfort, 1810 and Indotellina ‌Huber, Langleit & Kreipl, 2015 using the uranium/thorium method proved inconclusive, due to diagenesis. Corals (Porites sp. and Leptoria ‌phrygia ‌(Ellis & Solander, 1786)) collected close to the pool area where molluscs had been first collected, were subjected in 2014 to strontium isotope dating (University of Frankfurt, unpublished data). These returned ages between 2.78 and 4.74 million years. In order to confirm these results, some specimens of the molluscan assemblage were re-dated using the strontium isotope method. From the two selected Striatostrombus ‌blanci shells, were subsampled one superficial and one internal fragment, which yielded ages between 2.017 and 3.064 million years (N Strombus 1 and 2, see Montaggioni et al. 2023: supplementary material, table S4). Dating of two other Codakia ‌punctata ‌(Linnaeus, 1758) valves and of a merulinid coral sample gave similar ages, between 2.912 and 3.814 million years (N17 coral et N18 bivalve, see Montaggioni et al. 2023: supplementary material, table S4). As a summary, the age of the molluscan and coral assemblage ranges between 2.0 and 3.8 million years, revealing it is Plio-Pleistocene.

Upper Pleistocene Unit (Late ‌Pleistocene age)

Adjoining the Upper Pliocene feo unit, there are two reef systems along the north-western and eastern rim sides locally identified by Veeh (1966) as belonging to the last interglacial high sea stand about 120 000 yr BP. The newly dated U/Th coral specimens are affected by incipient diagenetic alteration. Accordingly, the newly obtained ages refer to “approximate ages”, not “absolute” or “true” ages (Montaggioni et al. 2023: supplementary material, table S3): at South Ofare, 135 005 ± 2289 cal. years BP (sample N27), at Tupana 132 067 ± 1686 cal. years BP (sample N72). These re-calculated ages are close to those related to the last interglacial high sea maximum, beginning at 128 000 cal. year BP (Murray-Wallace & Woodroffe 2014). Consequently, these reef units are regarded as belonging to the last interglacial period that is the chemiostratigraphic MIS 5e, i.e. Late ‌Pleistocene in age (Montaggioni et al. 2023). These cannot have developed from 135 000 years BP at the end of the low-sea stand (MIS 6: about 185 000 to 135 000 yr BP), that was during the Mid-Pleistocene (Murray-Wallace & Woodroffe 2014), at the time when sea level was probably lower than 100 m below its present position (Rohling et al. 1998; Masson-Delmotte et al. 2010).

Mid Holocene algal ridge on the reef flat ocean margin

An exposed algal crest, dated by the U/Th method, yielded an age of 4695 ± 0.052 years BP (sample N18, Montaggioni et al. 2023: supplementary material, table S3) corresponding to the Mid Holocene, emplaced at a time when the average ocean level was approximately 0.80 m higher than present. Similar algal features are found in most outer reef crests in the Tuamotu (Takapoto, Fakarava) and in the Society (Tetiaroa).

Overwiew of the depositional history of the atoll rim

The standard tectonic behaviour of mid-plate, mid-ocean volcanic islands is to sink after cessation of eruptive activity. This sinking (thermal subsidence) results mainly from the cooling and load increase of the underlying oceanic crust, which is no longer “heated” by the rise of magmatic asthenospheric (mantle) material. The uplift of seven islands in the north western part of the Tuamotu archipelago (Mataiva, Tikehau, Rangiroa, Kaukura, Niau, Anaa and Makatea) was recently demonstrated as resulting from the interplay between the northwestward migration of the Pacific lithospheric plate and the volcanic rejuvenation of the Society hotspot, resulting in a regional mantle bump (“asthenospheric bumping model” (Montaggioni et al. 2023, 2024). When the drifting plate that supports the seven atolls mentioned above, has entered the zone of influence of the Society hot spot (currently centered in the vicinity of Mehetia), the atolls have been uplifted incrementally over the last 2 million years, depending on their geographical position (Montaggioni et al. 2023, 2024). The exposed parts of the atoll rim at Niau are believed to have started to deposit about 4 Ma ago, during the Late ‌Pliocene times, when sea level was about 20 to 30 m above its present position. Then, according to the standard thermal subsidence effect, Niau has been drowned since this time, resulting in the deposition of Early Pleistocene reef generations. Niau is likely to have been uplifted not prior to 0.5 to 0.3 Ma, presumably in relation to the intense Mehetia activity (Montaggioni et al. 2023). Accordingly, the Plio-Pleistocene reef unit have undergone long periods of emergence during which karst erosion deeply altered them, resulting in the present geomorphic features. The uplift of the atoll has resulted in an isolation and drying of the lagoon until now.

MATERIAL

Material for the molluscan studies

One of the authors of the present paper (JL) collected in 2008 and 2009 a molluscan assemblage, composed of 120 species to be identified (identifications made by JT and JL) and listed by Salvat et al. (2018) and dated by Montaggioni et al. 2023 from the Plio-Pleistocene. This assemblage was dredged down to 4 meters deep from swamps near the Vaiohua sector which are presently locally called “la Piscine” (swimming pool; 16°08’22.32S, 146°23’14.09W; Fig. 1). The collection of this assemblage labelled “collection Letourneux, Niau” was housed at the Malacology Laboratory of the Muséum national d’Histoire naturelle in Paris. It gave rise to the description of three new gastropod species (Strombus ‌blanci ‌Tröndlé & Salvat, 2010, Terebra ‌niauensis ‌Tröndlé & Letourneux, 2011 and Turbo ‌fakaauensis ‌Tröndlé & Letourneux, 2012). New field researches on Holocene in 2020 (BS) have been carried in the localities of Aturona (samples N54 to N63), Vaiohua near the archeological platform (samples N103 to N106, N108, N90 to N94, TP1A and TP1B), Vaiohua on taro pit (sample N107) and in the modern material lagoon (Vaiohua near the shore, sample N95), see Figures 1 and 6 for the location. They allow us to collect other molluscan assemblages, which have been added to the collection, which is now housed in the collection of Palaeontology of the Muséum (sector fossil invertebrates).

Material for the radiometric studies

For radiocarbon analysis on Holocene material, four samples were taken at three points: Aturona (sample N57, Quidnipagum ‌palatam ‌Iredale, 1929), Vaiohua near the archeological platform (samples N103 and N121, Cerithium sp.) and Vaiohua taro pit (sample 107, Ctena ‌bella ‌Conrad, 1837).

METHODS

Observation of colored patterns from fossil molluscs under UV light

The observation of colour patterns on fossil shells in natural light is difficult, as the degradation of the pigments happens quickly after the death of the animal and continues also during fossilization. A solution to the problem is the use of ultraviolet light (UV), as the colour pattern of the fossil shells becomes visible with the exposure of wavelengths below 365 nm. In fact, the colored areas have not completely lost their pigments and can take on a white, beige, yellow or red color. These still pigmented surfaces contrast with a more depigmented background which, under UV light, often takes on a dark tint. This contrast between the different shell areas forms the color pattern. In the last fifteen years, many works have pointed out that the colour pattern of gastropods and bivalves can be easily revealed for the Cenozoic era and are important for their identification at species level (see Caze et al. 2011; Psarras et al. 2021 for more references). This technique is used herein to study fossil molluscs from Niau that potentially display a colored pattern (e.g., Conidae ‌J. Fleming, 1822). The shots were conducted using the same UV exposure (3600 Å). The photographs are presented as they were taken or sometimes in reverse image. We used Photoshop to create digital negative/inverse images of the photographs taken under UV light, thereby reconstructing what the shell would have looked like when the animal was alive.

Radiometric dating

The carbon-14 method is applicable to samples younger than 50 000 years. Radiocarbon ages are expressed in years BP by reference to 1950. Gastropods and bivalves extracted from the swamps and aroid taro culture pits were radiocarbon dated at the LMC14/LSCE laboratory (Gif-sur-Yvette). The sample preparation was conducted according to the protocol developed by Dumoulin et al. (2017). The measurements were carried out using Artemis accelerator mass spectrometer (AMS) (Moreau et al. 2020; Beck et al. 2024). The ages obtained were calibrated with the IntCAL Marine 20 curve (Heaton et al. 2020) and the Oxcal4.4 software (Bronk Ramsey 2001). The reservoir age correction used was made with ΔR 140 ± 20 years based on data obtained for French Polynesia (Petchey et al. 2008).

Abbreviations

RESULTS

Although surveys on Niau Atoll were carried out at different locations of the emerged reef rim and of the swamps and the lagoon, the results are presented site by site along a transect running from the fringing reef to the lagoon, located in the Ofare area, northwest of the atoll. On Figure 6, from an aerial Google Earth image, are delineated the different geomorphic features and units: outer reef slope, fringing reef-flat zone, conglomerate pavement, successive emerged, fossil reef units, coconut grove, feo zone (i.e. Plio-Pleistocene feo reef unit), swamp with the archaeological site of Vaiohua, coconut grove, beach, lagoon. Figure 7 gives a topographic profile across the same area, with location of the different geomorphic units. Figure 8 is a detailed morphological profile, restricted to the Vaiohua swamp site, the coconut grove and the lagoon margin. Due to the lack of precise topographical surveys, the ocean and the lagoon surfaces are considered to be at the same level.

Lagoon molluscan assemblages since the Late ‌Pliocene

SYSTEMATIC PALAEONTOLOGY

The taxa presented in this section follow the systematic classification given in Molluscabase website (https://www.molluscabase.org) for new species and those described previously.

Class‌ GASTROPODA Cuvier, 1795 Subclass‌ CAENOGASTROPODA L. R. Cox, 1960 Order‌ CAENOGASTROPODAincertae sedis Superfamily‌ Cerithioidea ‌J. Fleming, 1822 Family‌ Cerithiidae ‌J. Fleming, 1822 Subfamily‌ Cerithiinae ‌J. Fleming, 1822

Genus Cerithium ‌Bruguière, 1789CA729441-C20C-FF9B-FEAF-FBEAFDB1FB6010.5281/zenodo.19384208

Type species

Cerithium ‌adansonii ‌Bruguière, 1792, by subsequent designation (ICZN opinion 1109, 1978).

Cerithium ‌niauense ‌Merle, ‌n. sp.CA729441-C20C-FF87-FEB2-FA89FD7FFD51urn:lsid:zoobank.org:act:8A430C74-7DDA-4FEE-922E-7C9F2FD0D3D8

(Figs 9D-F; 11)

Cerithium ‌tenellum – Salvat et al. 2018: table 1 [non Cerithium ‌tenellum ‌G. B. Sowerby II, 1855].

Type material

Holotype

France • French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98401 (Letourneux coll.); H 20.1 mm (Fig. 11A-C).

Paratypes

France • 1 spm; same data locality as the holotype; Plio-Pleistocene; MNHN.F.A98402 (Letourneux coll.); H 19.1 mm (Fig. 11D-F) • 1 spm; Vaihuoa, near archeological platform (sample N106); Late ‌Holocene; MNHN.F.A98404 (Salvat coll.); H 15 mm (Fig. 11G, H) • idem; MNHN.F.A98405 (Salvat coll.); H 15.5 mm (Fig. 11I, J), • 1 spm; same locality and age (sample N108); MNHN.F.A98403 (Salvat coll.); H 20 mm (Fig. 11K, L) • 1 spm; idem (sample TP1A); MNHN.F.A98406 (Salvat coll.): H 20.8 mm (Fig. 11M, N) • 1 spm; idem (samples TP1A); MNHN.F.A98407 (Salvat coll.); H 16 mm (Fig. 11O, P) • 1 spm; idem (samples TP1B); MNHN.F.A98408 (Salvat coll.); H 23 mm (Fig. 11Q, R) • 1 spm; idem (samples TP1B); MNHN.F.A98409 (Salvat coll.); H 19.9 mm (Fig. 11S, T) • 1 spm; idem (samples TP1B); MNHN.F.A98410 (Salvat coll.); H 14.6 mm (Fig. 11U, V).

Additional material

France • 148 spm; same as the holotype; Plio-Pleistocene; MNHN.F.A98414 (Letourneux coll.) • 1 spm; Aturona (sample N58); Mid Holocenee; MNHN.F.A98417 (Salvat coll.) • 2 spm; idem (sample N57); MNHN.F.A98418 (Salvat coll.) • 4 spm; idem (sample N63); MNHN.F.A98420 (Salvat coll.) • 1 spm; Vaihuoa, near archeological platform (sample N90); Late ‌Holocene; MNHN.F.A98419 (Salvat coll.) • 4 spm; idem (sample N91); MNHN.F.A98425 (Salvat coll.) • 16 spm; idem (sample N106); MNHN.F.A98424 (Salvat coll.) • 8 spm; idem (sample TP1A); MNHN.F.A98427 (Salvat coll.) • 11 spm; idem (sample TP1B); MNHN.F.A98428 (Salvat coll.) • 1 spm; idem (sample N105); MNHN.F.A98411 (Salvat coll.); Fig. 9D • 1 spm; idem (sample 105); MNHN.F.A98412 (Salvat coll.); Fig. 9E • 1 spm; idem (sample 105); MNHN.F.A98413 (Salvat coll.); Fig. 9F • 11 spm; idem (sample N105); MNHN.F.A98423 (Salvat coll.) • 8 spm; idem (sample N93); MNHN.F.A98415 (Salvat coll.) • 1 spm; idem (sample N108); MNHN.F.A98421 (Salvat coll.) • 1 spm, idem (sample N104); MNHN.F.A98422 (Salvat coll.) • 3 spm; idem (sample N94); MNHN.F.A98416 (Salvat coll.) • 1 spm; idem (sample N103); MNHN.F.A98426 (Salvat coll.).

Etymology

From the type locality, Niau Atoll.

Type horizon

Plio-Pleistocene (molluscs assemblage), see Figs 7; 8.

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only know from the type locality, from Early Pliocene to Late ‌Holocene.

Description

Shell medium in size, subangulate, slightly cyrtoconoid. Protoconch unknown. Apical angle 34°. Height of last whorl: 43.5% of shell lenght. Sculpture on spire consisting of weak to moderately strong, slightly curved axial ribs that are swollen near the posterior suture. On last whorl, one varical node in opposite side of the outer lip. Early whorls with three primary beaded cords (P1-P3), P2 being more prominent. Secondary cords s1 and s3 occasionnal. Last whorl with three slightly beaded primary cords (P1-P3) more prominent than the anterior cords (P4-P7). Secondary cords s1, s2, s3 and s4 occasionnal. Under UV light, beaded cords fairer than the background. Height of aperture: 32.5% of shell lenght. Outer lip slightly thickened. Inner lip callused, weakly detached. Anal notch moderately deep. Parietal callus weak.

Comparisons

The sculpture of Cerithium ‌niauense ‌Merle ‌n. sp., is variable. In Plio-Pleistocene material, axial ribs can be more or less prominent and rows of cords on P1 to P3 can be more or less beaded. This variation allows to distinguish two extreme morphotypes, one characterized by well formed axial ribs (e.g., Fig. 11A-C) and one characterized by a beaded sculpture with low ribs (e.g., Fig. 11D-F). Transitional forms link these two morphotypes, showing that they belong to a same species. Holocene material displays a similar variation with two same extreme morphototypes (e.g., Fig. 11I, J; 11K, L) and no diagnostic characters allowing to distinguish a different species. All shells of C. ‌niauense ‌Merle ‌n. sp., are regularly slightly cyrtoconoid, their axial ribs are slightly curved and P2, the most prominent cord, is well distinct from P3. Plio-Pleistocene shells are creamy and sediment sometimes included in these shells is whitish, whereas Holocene shells are withish pale grey and display a dark grey sediment within their shell when present. Cerithium ‌tenellum ‌G. B. Sowerby II, 1855, originally described from Philippines, is reminiscent to C. ‌niauense ‌Merle ‌n. sp., but differs by having a conical shape, straigh axial ribs and P3 almost fused with P2, and no varical nodes. Cerithium ‌filosum ‌G. B. Sowerby II, 1865, also originally described from Philippines, displays a prominent beaded secondary cord s1 and has varical nodes lacking on the spire of C. ‌niauense ‌Merle ‌n. sp.,

Order‌ LITTORINIMORPHA Golikov & Starobogatov, 1975 Superfamily‌ Stromboidea ‌Rafinesque, 1815 Family‌ Strombidae ‌Rafinesque, 1815

Genus Gibberulus ‌Jousseaume, 1888CA729441-C210-FF87-FEA0-FD6AFCECFCC610.5281/zenodo.19384213

Type species

Strombus ‌gibberulus ‌Linnaeus, 1758 by monotypy.

Gibberulus ‌gibbosus ‌(Röding, 1798) CA729441-C210-FF87-FEA0-FC09FA92FED010.5281/zenodo.19384222

(Fig. 12A, B)

Lambis ‌gibbosa ‌Röding, 1798: 62, n°786-788.

Gibberulus ‌gibbosus – Wilson 1993: 158, pl. 21, fig. 12. — Salvat et al. 2018: table 1. — Maxwell et al. 2021: 100, figs 8-10.

Gibberulus ‌gibberulus ‌gibbosus – Boutet et al. 2020: 302.

Type material

Syntype

Philippines • Maxwell et al. (2021: 100) wrote that Röding (1798: 62, n°786-788) designated a holotype refering to the illustration of Martini (1777: pl. 27, fig. 794), but Röding (1798: 62) did not designate a holotype.

Type locality

Cebu Island, Philippines (Abbott 1960:144, fig. 8).

Figured material

France • 1 spm; French Polynesia, Niau Atoll, La Piscine”: 6°08’22.32S, 146°23’14.09W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98429 (Letourneux coll.); H 47.1 mm (Fig. 12A, B).

Other material

France • 21 spm; French Polynesia, Niau Atoll, La Piscine”: 6°08’22.32S, 146°23’14.09W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98430 (Letourneux coll.) • 3 spm; same; MNHN.F.A98431 (Letourneux coll.).

Distribution

Plio-Pleistocene, French Polynesia (this work) to today, Philippines, eastern Indonesian Archipelago, northeastern Papua New Guinea and associated Island chains (Maxwell et al. 2021: 104, fig. 11).

Description

See Maxwell et al. (2021: 99).

Comments

The figured material displays a uniform pinkish-yellow background interrupted by around seven small grey spiral bands. This residual pattern suggests that the coloured background was interrupted by unpigmented spiral bands. The colour pattern of Gibberulus ‌gibbosus is very variable (see Maxwell et al. (2021: figs 8-10), but it is also interrupted by white spiral bands. These white bands correspond to the small grey bands observed under UV light and indicate that the residual colour pattern on the Plio-Pleistocene fossils is strongly reminiscent of the colour pattern of the extant Gibberulus ‌gibbosus.

Genus Striatostrombus ‌Dekkers & S. J. Maxwell, 2018CA729441-C210-FF87-FCEB-FE08FACCF8ED

Type species

Striatostrombus ‌blanci ‌(Tröndlé & Salvat, 2010) by original designation.

Striatostrombus ‌blanci ‌(Tröndlé & Salvat, 2010) CA729441-C210-FF87-FCC6-FDA8FBD3F90C10.5281/zenodo.19390726

(Fig. 12C, D)

Strombus(s.l.)blanci ‌Tröndlé & Salvat, 2010: 616, figs 2A-G, J; 3; 4C-E. — Salvat et al. 2018: table 1.

Striatostrombus ‌blanci – Dekkers & Maxwell 2018: 224.

Type material

Holotype

France • French Polynesia, Niau Atoll, La Piscine”: 6°08’22.32S, 146°23’14.09W; Plio-Pleistocene (molluscs assemblage); MNHN-IM-2000-23289; H 34.5 mm.

Paratype

France • 1 spm; same as the holotype; EPHE coll.; H 36 mm • 1 spm; idem; Letourneux coll.; H 35 mm • 1 spm; idem; MNHN.F.A98433 (Tröndlé coll.); H 40 mm • 1 spm; idem; G. Kronenberg coll.; H 36 mm.

Figured material

1 spm; idem; MNHN.F.A98432; H 31.3 mm (Fig. 12C, D).

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7-8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only know from the type locality.

Description

See Tröndlé & Salvat (2010: 616) and Dekkers & Maxwell (2018: 224).

Comments

This species is close toStriatostrombus ‌micklei ‌(Ladd, 1972) from the Late ‌Miocene of Marshall Archipelago (Dekkers & Maxwell 2018). When S. ‌blanci was described, traces of a colour pattern were not researched. Under UV light, the studied material displays a uniform grey background (Fig. 12D) that suggests that the species was probably poorly pigmented and devoid of colour pattern.

Order‌ NEOGASTROPODA Wenz, 1938 Superfamily‌ Muricoidea ‌Rafinesque, 1815 Family‌ Muricidae ‌Rafinesque, 1815 Subfamily‌ Ergalataxinae ‌Kuroda, T. Habe & Oyama, 1971

Genus Drupella ‌Thiele, 1925CA729441-C210-FF87-FC70-F80EFA5AF86A

Type species

Drupa ‌cornus ‌Röding, 1798 by original designation.

Drupella ‌margariticola ‌(Broderip, 1833) CA729441-C217-FF81-FF48-F9CBFE55FDF1

(Fig. 12E-G)

Murex ‌margariticola ‌Broderip, 1833: 177.

Purpura ‌lineolata ‌Blainville, 1832: 206 [non Risso, 1826].

Purpura ‌violacea ‌Lesson, 1842: 186 [non Kiener, 1836].

Morula ‌margarticola– Salvat & Rives 1975: 317, fig. 216.

Cronia(Cronia)margariticola – Tröndlé & Houart 1992: 85, figs 5-7, 37.

Ergalatax ‌margariticola – Houart 2008: 105, figs 8, 14, 41-45.

Drupella ‌margariticola – Claremont et al. 2011: 105, fig. 1a. — Salvat et al. 2018: table 1. — Boutet et al. 2020: 373.

Type material

Lectotype

Australia • Designated by Emerson & d’Attilio (1981: 81); Lord Howe Island; BMNH1981146.

Figured material

France • 1 spm; French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98434 (Letourneux coll.); H 22.9 mm (Fig. 12E, F) • 1 spm; idem; MNHN.F.A98435 (Letourneux coll.); H 25.1 mm (Fig. 12G).

Other material

France • 4 spm; same data as the Figured material; MNHN.F.A98465 (Letourneux coll.).

Type locality

Australia, Tasman Sea, Lord Howe Island.

Distribution

Plio-Pleistocene (molluscs assemblage), French Polynesia, Niau Atoll to today, Indo-West-Pacific.

Description

See Tröndlé & Houart (1992: 85).

Comments

Two specimens display a residual colour pattern, but with a different degree of diagenesis. One is almost pristine (Fig. 12E, F) and its colour pattern is similar to that found in extant specimens. The other specimen exhibits yellow spots where the nodules are, that indicates strongly pigmented nodules (Fig. 12G). Unpigmented areas correspond to spiral grooves and intervarical spaces. This pattern is reminiscent to living specimens having brown or black nodules interrupted by fairer or white spiral grooves.

Superfamily‌ Conoidea ‌J. Fleming, 1822 Family‌ Conidae ‌J. Fleming, 1822

Genus Conus ‌Linnaeus, 1758CA729441-C216-FF81-FE86-FC8AFE48FC0110.5281/zenodo.19384234

Type species

Conus ‌marmoreus ‌Linnaeus, 1758, by subsequent designation (Children 1823).

Subgenus Conus Linnaeus, 1758

Conus (Conus) letourneuxi ‌Merle, ‌n. sp.urn:lsid:zoobank.org:act:5DDF566A-05C5-43D7-B2D5-BB49C5189FC7CA729441C216FF81FF4CFC6BFA47FDF110.5281/zenodo.19384242

(Fig. 13A-D)

Conus ‌marmoreus – Salvat et al. 2018: table 1 [non Conus ‌marmoreus ‌Linnaeus, 1758].

Type material

Holotype

France • French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98436 (Letourneux coll.); H 70.5 mm.

Etymology

Dedicated to Jean Letourneux.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7; 8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only known from the type locality.

Description

Shell moderately large, with very low conical spire. Apical angle 118°. Teleoconch of 9 whorls, whorl tops smooth delimited by a shoulder very slightly lower than the suture. Suture moderately impressed. Subsutural sinus deep, strongly curved, strongly asymmetrical. Last whorl with concave subsutural platform, slighlty angled at shoulder placed below suture, regularly conical below, position of maximum diameter close below shoulder, not constricted at base. Siphonal fasciole weakly developed. Weak, close set spaced cords from the base to the center of last whorl and fasciole. Aperture relatively narrow with parallel sides, hardly widening abapically; siphonal canal short. Colour pattern poorly preserved consisting large dark triangular spots surrounded by light yellow fluorescent bands under UV light.

Comparisons

The residual colour pattern of Conus(Conus)letourneuxi ‌n. sp. (Fig. 13C, D) is reminicent to that of Conus(Conus)marmoreus ‌(Linneaus, 1758),Conus(Conus)bandanus ‌Hwass in Bruguière, 1792 and Conus(Eugeniconus)marchionatus ‌Hinds, 1843. The shells of C.(C.)marmoreus and C.(C.)bandanus have a crenulated spire, whereas that of C.(C.)letourneuxi ‌n. sp. is smooth. C.(E.)marchionatusdisplays a smooth spire, but it is flatter than that of C.(C.)letourneuxi ‌n. sp. and the shape of its triangular spots is more rounded.

Subgenus Tesselliconus ‌da Motta, 1991CA729441-C216-FF83-FC01-FD29FDAAF94C

Type species

Conus ‌tessulatus ‌Born, 1778 by original designation.

Conus (Tesselliconus) georgesrichardi ‌Merle, ‌n. sp.urn:lsid:zoobank.org:act:00915CC5-39F5-478D-84BA-87551894B565CA729441-C216-FF83-FCC0-FCC9FDAAF94C

(Figs 13E-Q; 14A-L; 15A-D)

Conus ‌eburneus – Salvat et al. 2018: table 1 [non Conus ‌eburneus ‌Hwass in Bruguière, 1792].

Conus ‌litteratus – Salvat et al. 2018: table 1 [non Conus ‌litteratus ‌Linnaeus, 1758].

Conus ‌pertusus – Salvat et al. 2018: table 1 [non Conus ‌pertusus ‌Hwass in Bruguière, 1792].

Conus ‌tessulatus – Salvat et al. 2018: table 1 [non Conus ‌tessulatus ‌Born, 1778].

Type material

Holotype

France • French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98437 (Letourneux coll.); H 43.4 mm (Figs 13E-H; 15A, B).

Paratypes

France • 1 spm; same data as the holotype; MNHN.F.A98438; H 39.4 mm (Fig. 13I, J) • 1 spm; idem; MNHN.F.A98439; H 89.6 mm (part of the last whorl, Fig. 13K) • 1 spm; idem; MNHN.F.A98440; H 35.9 mm (Fig. 13L-O) • 1 spm; idem; MNHN.F.A98441; H 34 mm (Fig. 13P, Q) • 1 spm; idem; MNHN.F.A98442; H 29.6 mm (Fig. 14A, B) • 1 spm; idem; MNHN.F.A98443; H 28.1 mm (Fig. 14C) • 1 spm; idem; MNHN.F.A98444; H 22 mm (Fig. 14D, E) • 1 spm; idem; MNHN.F.A98445; H 36.7 mm (Fig. 14F, G) • 1 spm; idem; MNHN.F.A98446; H 35.6 mm (Fig. 14H, I; 15C, D) • 1 spm; idem; MNHN.F.A98447; H 23 mm • 1 spm; idem; MNHN.F.A98448; H 23.6 mm (Fig. 14J-L). All paratypes from Letourneux coll.

Additional material

France • 3 spm; same data as the holotype; MNHN.F.A98449 (Letourneux coll.).

Etymology

Dedicated to Georges Richard.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7; 8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only know from the type locality.

Description

Shell large (MNHN.F.A98439 (Fig. 13K) part of the last whorl = 89.6 mm), with low coeloconoid to conical spire. Apical angle 135°. Teleoconch of 7-8whorls, whorl tops smooth except for close-set, comma-shaped growth lines, concave, delimited by shoulder raised very slightly below suture. Suture weakly impressed. Subsutural sinus shallow, slightly curved, moderately asymmetrical. Last whorl with horizontal, flat subsutural platform, smoothy angled at shoulder placed almost at suture, regularly conical below, position of maximum diameter close below shoulder, not constricted at base. Siphonal fasciole weakly developed; a few weak, widely spaced cords over base and fasciole, strengthening slightly abapically. Aperture relatively narrow with parallel sides, widening abapically; siphonal canal short. Under UV light, residual colour pattern consisting of two components: (1) pale, yellow-white fluorescent spots, spirally aligned and (2) dark, non-fluorescent background. Small rectangular spots of unequal size, distributed on the last whorl in four zones from shoulder to base. Zone a (first posterior quarter of whorl): 3-4 rows of sparse dots; zone b (second posterior quarter of whorl): 3-6 rows of close-set dots; zone c (first anterior quarter of whorl: 2-3 spaced rows of sparse dots; zone c (second anterior quater of whorl): 4-8 rows of more or less spaced dots (Fig. 15A-D).

Comparisons

Among French Polynesian Conidae bearing spiral rows of dots, C.(Tesselliconus)georgesrichardi ‌n. sp. may be compared with Conus(Elisaconus)litteratus ‌(Linnaeus, 1758), C.(Tesselliconus)tessulatus ‌Born, 1778 and C.(T.)eburneus (Hwass in Bruguière, 1792). C.(E.)litteratus differs in having a planispiral spire, a narrow, concave subsutural platform and a shoulder placed above the suture. Conus(E.)litteratus displays around 20-25 row of dots, instead 15-18 inC.(T.)georgesrichardi ‌n. sp. In addition, the rows are regularly aligned from the shoulder to the base on last whorl, whereas those of C.(T.)georgesrichardi ‌n. sp. are organised in four zones (a to d). The shell shape of Conus(T.)tessulatus is reminiscent to that C.(T.)georgesrichardi ‌n. sp. and as in the Plio-Pleistocene species, the rows of dots are organised in four zones (Fig. 15E, F). However, Conus(T.)tessulatus species differs clearly by having in elongated larger dark dots. The colour pattern of C.(T.)erburneus consists in four similar zones of spiral rows of dots as in C.(T.)georgesrichardi ‌n. sp. (Fig. 15G, H) However, the dots of C.(T.)georgesrichardi ‌n. sp. are smaller and more close set in the zone b. Moreover, the spire of C.(T.)georgesrichardi ‌n. sp. can be more conical, the shell shape is wider and some gerontic individuals can reach a larger size (H more than 89 mm).

Family‌ Terebridae ‌Mörch, 1852 Subfamily‌ Terebrinae ‌Mörch, 1852

Genus Oxymeris ‌Dall, 1903CA729441-C214-FF83-FE91-F8ECFF11F86A10.5281/zenodo.19384249

Type species

Buccinum ‌maculatum ‌Linnaeus, 1767 by original designation.

Oxymeris ‌niauensis ‌(Tröndlé & Letourneux, 2011)CA729441-C214-FF83-FCFB-FF48FAE0F9CC10.5281/zenodo.19384257

(Fig. 14M-P)

Terebra ‌niauensis ‌Tröndlé & Letourneux, 2011: 87, figs 1-5, 8, 9.

Terebra ‌niauensis — Salvat et al. 2018: table 1.

Type material

Holotype

France • French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN-IM-2000-23684; H 96.5 mm.

Paratypes

France • 1 spm; same data as the holotype; EPHE coll.; H 89.55 mm • 9 spm; idem; MNHN-IM-2000-23686; H 78 mm, 81.6 mm, 74 mm, 62.7 mm, 62 mm, 60.4 mm, 55 mm, 50.7 mm, 48.9 mm • 1 spm; idem; Jean Tröndlé coll.; H: 61.2 mm • 1 spm; idem; Letourneux coll.; H 86.1 mm (Fig. 19N-P) • 1 spm; idem; G. Paulay coll.; H 84 mm • 1 spm; idem; A. Waren coll.; H 79.1 mm • 1 spm; idem; Mairie de Niau coll.; H 87.5 mm • 1 spm; idem; M. Boutet coll.; H 87.8 mm • 1 spm; idem; G. Kronenberg coll.; H 60.6 mm.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7-8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Figured material

One paratype (Letourneux coll.), Fig. 19M-P.

Distribution

Only known from the type locality.

Description

See Tröndlé & Letourneux (2011: 88).

Comments

Tröndlé & Letourneux (2011) noted that UV light revealed only a few spots under the suture of the holotype. On the examined paratype, a dark band is also present under the suture of the penultimate and the last whorl of the specimen examined. These authors found strong shell similarities with Oxymeris ‌gouldi ‌(Deshayes, 1857), today Hawaii. O. niauensis looks also allied toOxymeris ‌caledonica ‌(G. B. Sowerby III, 1909), today New Caledonia. Therefore, O. niauensis seems better placed in the genusOxymeris ‌Dall, 1903.

Subclass‌ HETEROBRANCHIA Burmeister, 1837 Order‌ CEPHALASPIDEA P. Fischer, 1883 Superfamily‌ Bulloidea ‌Gray, 1827 Family‌ Bullidae ‌Gray, 1827

Genus Bulla ‌Linnaeus, 1758CA729441-C214-FF83-FC75-F9ECFBC9F95C10.5281/zenodo.19384264

Type species

Bulla ‌ampulla ‌Linnaeus, 1758 by subsequent designation (Gray 1847).

Bulla ‌niauensis ‌Merle ‌n. sp.CA729441-C214-FF8E-FC75-F88CFD49F98Furn:lsid:zoobank.org:act:8C774DB3-F7BE-4DD8-838C-01E30AA984D9

(Fig. 16)

Bulla ‌vernicosa – Salvat et al. 2018: table 1 [non Bulla ‌vernicosa ‌Gould, 1859].

Type material

Holotype

France • French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98450 (Letourneux coll.); H 25.4 mm (Fig. 16A-E).

Paratypes

France • 1 spm; same data as the holotype; MNHN.F.A98452 (Letourneux coll.); H 25.7 mm • 1 spm; idem; MNHN.F.A98451 (Letourneux coll.), H 24.5 mm (Fig. 16F, G).

Additional material

France • 3 spm; same data as the holotype; MNHN.F.A98453 (Letourneux coll.).

Etymology

From the type locality Niau (French Polynesia).

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7; 8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”, 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only know from the type locality.

Description

Shell thick, shape subquadrangular, wider anteriorly. Parietal callus thin; collumella thick. Spire aperture wide. Outer lip straight posteriorly, rounded anteriorly. Under UV light, residual pattern composed of two levels of residual pigmentation: a lighter background and dark stripes from wavy to zigzagging.

Comparisons

Bulla ‌ampulla ‌(Linnaeus, 1758) resembles Bulla ‌niauensis ‌Merle ‌n. sp., but differs by having a subquadrangular shape. The colour pattern displays mainly a fair background and darker dots and tending to collapse in small dots of irregular shape. Bulla ‌vernicosa ‌A. Gould, 1859 is more quadrangular than Bulla ‌niauensis ‌n. sp. and its outer lip is straighter anteriorly. The colour pattern of Bulla ‌vernicosa is fair brown, with darker small dots. In reverse UV light, the pattern of Bulla ‌niauensis ‌n. sp. is also fair brown, but it bears dark stripes from wavy to zigzagging, lacking in Bulla ‌vernicosa (see Malaquias & Reid 2008: fig. 27L-Q).

Class‌ BIVALVIA Linnaeus, 1758 Order‌ CARDIIDA A. Férussac, 1822 Superfamily‌ Cardioidea ‌Lamarck, 1809 Family‌ Cardiidae ‌Lamarck, 1809 Subfamily‌ Fraginae ‌R. B. Stewart, 1930

Genus Lunulicardia ‌J. E. Gray, 1853CA729441-C219-FF8E-FEA1-F9ACFCE8F90410.5281/zenodo.19384272

Type species

Cardium ‌retusum ‌Linnaeus, 1767 by monotypy.

?Lunulicardia ‌distorta ‌Merle, ‌n. sp.CA729441-C219-FF8F-FEA4-F94CFB72F86Durn:lsid:zoobank.org:act:24555983-F607-4A6A-A048-4767EA62CCEE

(Fig. 17A-H)

Lunulicardia sp. —Salvat et al. 2018: table 1.

Type material

Holotype

France • 1 spm (right valve); French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A99068 (Letourneux coll.); DVL 18 mm (Fig. 17A, B, G).

Paratypes

France • 1 spm (right valve); same data as the holotype; MNHN.F.A99821 (Letourneux coll.); DVL 21.8 mm (Fig. 17E, F) • 1 spm (left valve); MNHN.F.A99822 (Letourneux coll.); DVL 29.9 mm (Fig. 17C, H) • 1 spm (left valve); MNHN.F.A99823 Letourneux coll.); DVL 28.7 mm (Fig. 17D) • 6 spm (2 right valves, 4 left valves); MNHN.F.A99055 (Letourneux coll.); DVL 21.8 mm.

Etymology

From the Latin adjective distortus (meaning distorted), because of the strongly curved the posterior area of the shell.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7; 8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”, 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only known from the type locality.

Description

Shell moderately thin, strongly inflated in older specimens; strongly oblique, with a strong posterior sulcus. Shell up to 29.9 in DVL and 23.5 mm in APL. Anterior margin obliquely rounded; ventral margin oblique, descending toward carina; posterior margin strongly sinuate concave in its center. Carina sharply expressed, rounded and smooth. Shell equivalve and inequilateral with angulate, weakly prosogyrous umbones placed in anterior half and extending above dorsal line. Shell surface densely radially sculptured, with 13-18 anterior ribs and 10-12 porterior ribs. Anterior ribs low, rather flat, slightly split by a central groove and separated by narrow interspaces less than 3/4 rib in breadth. Posterior ribs low becoming larger near the ventral margin. Pallial line entire, positioned moderately close to the ventral margin and connecting two medium-sized subovate scars. Shell margin finely crenulate ventrally, but with coarser crenulations on posterior margin. Posterior part well delineated from anterior by carinal groove. Hinge line strong and rather thick, with two cardinal teeth and two prominent lateral teeth. Posterior lateral tooth in right valve and anterior lateral in left valve strong.

Comparisons

The Plio-Pleistocene assemblage from Niau contains two species of Fraginae, Fragum ‌fragum ‌(Linnaeus, 1758) and ?Lunulicardia ‌distorta ‌Merle ‌n. sp., Fragum ‌fragum is less carinate, its posterior margin is slightly convex and the surface of its ribs is squamous (see Fig. 9M-O). In the living fauna from French Polynesia, Boutet et al. (2020) report three other species of Fragum ‌Röding, 1798: F. ‌mundum ‌(Reeve, 1845), F. ‌sueziense ‌(Issel, 1869) and F. ‌whitleyi ‌Iredale, 1919. They differ easily from ?Lunulicardia ‌distorta ‌Merle ‌n. sp., by their weak carina and their convex posterior margin. Members of Lunulicardia ‌J. E. Gray, 1853 (type species: Cardium ‌retusum ‌Linnaeus, 1767 by monotypy, present day: Indo-West Pacific from Japan to Australia to South Africa) are reminiscent of ?Lunicardia distorta Merle, in their angulate carina, but have a concave posterior margin. Americardia ‌Stewart, 1930 (type species: Cardium ‌medium ‌Linnaeus, 1758 by original designation, present day, Western Atlantic) has a weakly angulate carina, more ribs (22-25 anterior ribs), but is slightly reminiscent of ?Lunulicardia ‌distorta ‌Merle ‌n. sp., in its weakly concave posterior margin. Americardia ‌lightbourni ‌Lee & Huber, 2012 from Bermuda Island displays a very concave posterior margin as it is in ?L. ‌distorta ‌n. sp., but differs by many other characters (weakly angulate carina, numerous ribs with a squamous surface). Finally, ?L. ‌distorta ‌n. sp. is a very peculiar species for the Tuamotu archipelago. Its attribution to Lunulicardia is also uncertain as its posterior margin is strongly concave, whereas it is convex in species usually attributed to this genus.

Superfamily‌ Tellinoidea ‌Blainville, 1814 Family‌ Tellinidae ‌Blainville, 1814 Subfamily‌ Tellininae ‌Blainville, 1814

Genus Tellinella ‌Mörch, 1853CA729441-C21F-FF88-FE85-FEC8FE3FFE4210.5281/zenodo.19384279

Type species

Tellina ‌virgata ‌Linnaeus, 1758, by subsequent designation (Schmidt F. C. 1818).

Tellinella cf. virgata ‌(Linnaeus, 1758) CA729441-C21F-FF88-FF58-FE67FCE2FA51

(Fig. 18A-C)

Tellina ‌virgata – Salvat et al. 2018: table 1.

Figured material

France • 1 left valve; French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98454 (Letourneux coll.); APL 69.7 mm (Fig. 18A-C).

Other material examined

France • 2 spm; same data as Figured material; MNHN.F.A98455 (Letourneux coll.)

Description

Shell rather large for family. Shape ovate-slightly elongate and subequilateral. Sculpture of commarginal striae becoming slightly oblique near posterior end; posterior slope with well distinct commarginal striae; anterior lateral tooth elongate, rather thick, moderately close to cardinals; posterior lateral tooth rather thick, distant from cardinals; pallial sinus poorly visible. Residual colour pattern uniform showing poorly defined concentric bands crossed by several very weak transverse lines more visible on the anterior part of valve.

Comments

This shell (Fig. 18A-C) resembles living Tellinella ‌virgata (see Fig. 18D-E) but its shape is more ovate with a higher dorso-ventral lenght. In addition, its residual colour pattern don’t display well large transverse dark bands, as observed in the syntype (P-Z 0010893) of the Linnean collection [https://www.linnean.org/research-collections/linnaean-collections] and as in other specimens (Fig. 18D, E). Thus, the attribution of this specimen to Tellinella ‌virgata is provisional and is proposed with some doubts.

Genus Indotellina ‌M. Huber, Langleit & Kreipl, 2015CA729441-C21F-FF88-FF02-F989FF16F90010.5281/zenodo.19384283

Type species

Tellina ‌chariessa ‌A. E. Salisbury, 1934 by original designation.

Indotellina ‌fakaauensis ‌Merle, ‌n. sp.CA729441-C21F-FF8A-FEA0-F928FAB1F9CFurn:lsid:zoobank.org:act:AF800AD8-3ACD-488C-8306-9EF6C41342BE

(Fig. 18F-L)

Soletellina sp. – Salvat et al. 2018: table 1.

Soletellina sp. – Salvat et al. 2020: 27, pl. 2, fig. 4.

Type material

Holotype

France • 1 complete spm (right and left valves); French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A99067 (Letourneux coll.); APL 93.2 mm (Fig. 18F-I).

Paratypes

France • 1 complete spm; same data as the holotype; MNHN.F.A99069 (Letourneux coll.); APL 99.8 mm (Fig. 18J, K) • 1 complete spm; MNHN.F.A99824 (Letourneux coll.); APL 104 mm (Fig. 18L) • 1 complete spm with a broken right vave; MNHN.F.A99978 (Letourneux coll.) • 5 spm; MNHN.F.A99151 (Letourneux coll.).

Etymology

From the type locality, Fakaau: Paumotu name for Niau.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7-8).

Type locality

French Polynesia, Niau Atoll, “La Piscine”: 6°08’22.32”S, 146°23’14.09”W.

Distribution

Only know from the type locality.

Description

Larger shell extending to 104 mm in APL and to 55 mm in DVL, elongate, moderately inequilateral, equivalved, subsolid, rather compressed and with weak flexure posteriorly. Umbo slightly behind middle, rather inconspicuous and blunt. Anterior margin broadly rounded; ventral margin elongate, slightly convex, rising arcuately posteriorly; anterior dorsal margin straight to gently convex, fairly elongate, and gently descending; posterior dorsal margin elongate, slightly descending and weakly convex; posterior margin weakly biangulate, concave ventrally. Surface of shell smooth with only concentric growing striae. Ligament area thin and shallow on anterior dorsal margin and deeper and slightly wider on posterior dorsal margin; weakly developed escutcheon; lunule poorly developed. Commissure line of the ventral margin slightly twisted in its posterior part. Hinge line well developed. In left valve, cardinal complex consisting of an anterior, strong bifid tooth with subequal lobes, and of a posterior, elongate and thin laminate tooth; anterior lateral tooth obsolete; posterior lateral tooth obsolete, distal to cardinal complex; cardinal hinge plate extensive, particularly anteriorly. In right valve, cardinal complex consisting of a posterior, slightly skewed, well-developed, bifid cardinal tooth with subequal lobes, and of anterior slightly thickened, laminate, cardinal tooth; anterior lateral tooth small; posterior lateral tooth obsolete and distal to cardinal complex; anterior lateral tooth closer to cardinal complex. Muscle scars moderately well impressed; anterior and posterior adductor muscles scar irregularly semilunate. Pallial sinus subequal in opposite valves; pallial line poorly distinct.

Comparisons

This species was first identified as a Psammobiidae ‌J. Fleming, 1828 of the genus Soletellina ‌Blainville, 1824, a junior synonym of Hyatula Modeer, 1793 (type species Hiatula ‌dyphos ‌(Linnaeus, 1771) by subsequent designation. Hyatula ‌diphos (= Soletellina ‌radiata ‌Blainville, 1824) is a present-day Indo-West Pacific species and is reminiscent of Indotellina in its smooth surface and in its elongate and inequilateral shape with a posterior margin longer than the anterior margin. Hiatula ‌diphos differs from Indotellina by lacking lateral tooth and by having a moderately long nymph. Moreover, its posterior margin is less angular and more convex than that of Indotellina. Until now, Indotellina was only known by its type species, Indotellina ‌chariessa ‌A. E. Salisbury, 1934 [junior synonym of Tellina ‌elegans ‌W. Wood, 1828, not Deshayes (1824)]. It is a present-day Indo-West Pacific species but there is an unpublished record in the Pliocene from Niué atoll in Western Polynesia (see https://www.gbif.org/occurrence/1064827107 and Paulay & Spencer 1992 for the geological context). According to Boutet et al. (2020), this species is missing in the present-day Polynesian fauna. Indotellina ‌chariessa is very similar to Indotellina ‌fakaauensis ‌Merle ‌n. sp., and both species share an angulate posterior margin and a hinge with lateral tooth. However, Indotellina ‌fakaauensis can be distinguished by its more rectilinear ventral margin, its less angulate posterior margin and its more convex dorso-posterior margin. Indotellina ‌fakaauensis is located just outside the geographical range of I. ‌chariassae and it is possible that its presence in the Tuamotu Archipelago results from a Pliocene speciation phase separating both species and followed by its extinction.

Order‌ VENERIDA Gray, 1854 Superfamily‌ Veneroidea ‌Rafinesque, 1815 Family‌ Veneridae ‌Rafinesque, 1815 Subfamily‌ Gouldiinae ‌R. B. Stewart, 1930

Genus Gafrarium ‌Röding, 1798CA729441-C21D-FF8A-FC60-F9EAFBF7F96010.5281/zenodo.19384290

Type species

Venus ‌pectinata ‌Linnaeus, 1758 by subsequent designation (Dall 1902).

?Gafrarium ‌troendlei ‌Merle, ‌n. sp.CA729441-C21D-FF8B-FC12-F889FC20FD11urn:lsid:zoobank.org:act:2AB9871C-6D0C-4858-A136-0CD4E1AF64E4

(Fig. 19)

Gafrarium sp. –Salvat et al. 2018: table 1.

Type material

Holotype

France • 1 left valve; French Polynesia, Niau Atoll, “La Piscine”; 6°08’22.32”S, 146°23’14.09”W; Plio-Pleistocene (molluscs assemblage); MNHN.F.A98456 (Letourneux coll.); APL 53 mm (Fig. 19A-D).

Paratypes

France • 10 left valves, 6 right valves, one complete specimen (two valves); same data as the holotype; MNHN.F.A98458 (Letourneux coll.) • 1 spm, MNHN.F.A98457 (Letourneux coll.); APL 52 mm (Fig. 19E, F).

Etymology

Dedicated to Jean Tröndlé.

Type horizon

Plio-Pleistocene (molluscs assemblage) (see Figs 7; 8).

Type locality

French Polynesia, Niau Atoll, La Piscine”: 6°08’22.32S, 146°23’14.09W.

Distribution

Only known from the type locality.

Description

Shell weakly suborbicular, solid, thick; umbones flat, prosogyrate; lunule elongate heart-shaped, poorly raised, weakly delineated by incised line; escutcheon poorly defined, narrow; anterodorsal margin short, rounded terminally; ventral margin convex slightly angulate near posterior margin; posterodorsal margin moderately convex, angulate at its posterior termination. Sculpture radially, divaricately ribbed at early stages of growth and of dense concentric ribs at later stage of growth. Hinge of left valve with anterior lateral tooth solid, thick, peg-like; anterior cardinal very thin, separated from median cardinal by narrow V-shaped socket; median cardinal thick, oblique, raised; posterior cardinal free, thin, elongate and oblique; posterior lateral thin, parallel to nymph. Hinge of right valve with broad anterior pit, anterior lateral short, anterior cardinal short, slightly oblique, median cardinal, thick, peg-like, slightly oblique; posterior cardinal oblique, peg-like; posterior lateral, parallel to nymph. Anterior muscle adductor scars trapezoidally shaped, posterior adductor scars ovate. Pallial line wide; pallial sinus diminutive. Residual colour pattern formed of radial, narrow and more or less wavy yellow fluorescent lines (Fig. 18C).

Comparisons

This enigmatic species was previoulsy identified asCirce ‌plicatina ‌(Lamarck, 1818) in collection and as Gafrarium sp. (Salvat et al. 2018). Valves of Circe ‌plicatina are more trigone in shape, their sculpture is less divaricate near the umbo, their cardinal teeth are less solid, less thick and their anterior pits are less broad. Early stages of growth of shells of Circe ‌scripta ‌(Linnaeus, 1758), type species of Circe ‌Schumacher, 1817 resemble those of Circe ‌plicatina and differ from those of ?Gafrarium ‌troendlei ‌n. sp. in having only concentric ribs. In addition, both species of Circe differs by having more compressed shells. The early stages of growth of ?Gafrarium ‌troendlei ‌Merle ‌n. sp., are reminscent to G. ‌harteae and other species of Gafrarium ‌Röding, 1798 in having a dominant radial sculpture of ribs tending sometimes to be divaricated. However, ?G. ‌troendlei ‌Merle ‌n. sp., can be easily distinguished from G. ‌harteae ‌Huber, 2010 and the type species of the Gafrarium ‌Röding, 1798, Gafrarium ‌pectinatum ‌(Linnaeus, 1758), by its a dominant concentric sculpture and by its smooth, not crenulated ventral margin (see Fig. 9J-L). Gafrarium ‌tumidum ‌Röding, 1798, currently present on part of the south-west coast of Tahiti from Port Phaëton to Vairao, differs by its stronger radial sculpture and by the shape of its cardinal plate and muscle impressions. Among other species of Gafrarium, a dominant concentric sculpture is found in G. ‌eaquivocum ‌(Holten, 1802). Therefore, we prefer attribute ?Gafrarium ‌troendlei ‌Merle ‌n. sp., to Gafrarium than Circe, but this attribution is provisional, because the characters of this species are not fully typical of Gafrarium.

DISCUSSION

The absolute radiometric dates obtained make it possible to pinpoint the timing of events in the Niau lagoon since the Late ‌Pliocene. In addition, the updating of the faunal content from the Plio-Pleistocene and the identification of Holocene assemblages make it possible to reconstruct the evolution of malacological assemblages up to the contemporary period. Thus, the following discussion is therefore divided into the following sections 1°) Paleoenvironment changes of the Niau atoll from Plio-Pleistocene to the Holocene and its consequences on the molluscan assemblages; 2°) Characteristics of the mollusc assemblage from the Plio-Pleistocene; 3°) Characteristics of the mollusc assemblage of the Holocene above the limestone crust; 4°) Characteristics of the mollusc assemblage of the modern lagoon.

Paleoenvironment changes of the Niau atoll from the Plio-Pleistocene to the Holocene and its consequences on the molluscan assemblages

The compositional attributes of the coral-molluscan thanatocenoses of Plio-Pleistocene are clearly those of a lagoonal environment, suggesting continuous water exchanges between the lagoon and the open ocean. These exchanges may have occurred through passes and channels (hoa), probably favoured by the fact that, during the Late ‌Pliocene, higher sea stands were about + 20 m above present sea level (Grant et al. 2019) and a rich fauna of molluscs developed there as evidenced by the 92 species identified (Table 1). The coral-molluscan beds were later occluded by deposition of sandy sediments beneath the limestone crust (caliche), 2.505-2.245 Ma (Early Pleistocene). From about 0.5 Ma, the atoll started to be uplifted. Exchanges between ocean and lagoon waters may have occurred periodically over the Pliocene feo edifices of the atoll, as sea level was higher than present, especially, during MIS 11 to 9 stages (respectively about 400 000 and 320 000 yr BP). This uplift of the coral edifices allows the development of a malacological fauna with very few species, which experienced compositional changes during the Holocene (see Table 2) in conjunction with the reduction of the surface of the lagoon and the revegetation of its border. There is, however, a gap in deposition and associated mollusc assemblages between the Pleistocene and the Mid Holocene. This may be due to a lack of deposition or subsequent erosion at the site. The persistence of several species from both assemblages, such as Ctena ‌bella and Cerithium ‌niauense ‌Merle ‌n. sp., , nevertheless proves that during this intermediate period, these species continued to live in lagoon localities others than those surveyed at Vaiohua. The next and final stage refers to the current lagoon with particular hydrological characteristics. This lagoon was inhabited by surviving species and species introduced by man. In addition to the molluscan species inhabiting the entire lagoonal zone, some species limited to the "marite" spots in response to cooler ocean waters and to salinity close to 36 g/l (Quidnipagus ‌palatam ‌Iredale, 1929, Gibberulus gibbosus (Röding, 1798),Notocochlis ‌gualteriana ‌(Récluz, 1844) and Longchaeus ‌maculosus ‌(Lamarck, 1822) are probably more recent according to present sea level in the ocean and the lagoon and the porosity of the karstic edifice of Niau.

Characteristics of the Plio-Pleistocene molluscan assemblage

Characteristics of the Holocene molluscan assemblage above the Limestone Crust

In the Holocene assemblage (taro pits excluded, see Table 2), Cerithium ‌Bruguière, 1789, the most abundant genus with three species (Cerithium ‌columna ‌G. B. Sowerby I, 1834, C. ‌rostratum ‌G. B. Sowerby II, 1855 and C. ‌niauense ‌Merle ‌n. sp.,) corresponds to gastropods, which are living in the intertidal zone and feed off the microflora covering calcareous substrates as the mentioned caliche or coarse sediments. Indeed, their favorite habitat is that of supra-littoral calcareous flagstones, inward of reef flat zones or, more particularly, on the edges of water exchange channels (hoa) between motu which are topographically quite similar to the limestone crust. Other species, mainly bivalves (Ctena ‌Mörch, 1861, Gafrarium Röding, 1798 andFragum ‌Röding, 1798) are indicative of fine to coarse sediments in which these were inhabiting. This molluscan assemblage is typical of lagoonal habitat, with limestone substrates for gastropods and coarse and fine sand for bivalves.

Compared to the thanatocenosis of molluscs collected beneath the limestone crust, this assemblage above the said crust is ten times less rich, nine species against 92 species. In addition to this quantitative impoverichment, comparison of the two assemblages allows some additional comments. Although these two assemblages inhabited the lagoon after an interval of around two million years (Early Pleistocene deposits beneath the crust and Holocene deposits above the crust), we note that among the most abundant species present beneath the crust (see Table 1, column abundances, code D = more more than 100), Cerithium ‌punctatum ‌Bruguière, 1792,Clypeomorus ‌bifasciata ‌(G. B. Sowerby II, 1855) and Finella ‌pupoides ‌A. Adams, 1860 no more are present above the crust. The disappearance of Cerithium ‌punctatum from Holocene sediments is temporary, however, since the species has reappeared in the present-day lagoon. Contrary Ctena ‌bella ‌(Conrad, 1837) andCerithium ‌niauense ‌Merle ‌n. sp., are still present as well as Fragum ‌fragum ‌(Linnaeus, 1758), see Table 2. Such a faunal impoverishment is likely to have been caused by uplift of the atoll, thus resulting in the connection failure between the lagoon and the open sea.

The few species collected on the taro pit of Late ‌Holocene age (Tables 2; 3) are just suffered an impoverichment when compared to those collected above the limestone crust, noting the maintenance of Ctena ‌bella and Cerithium ‌niauense ‌Merle, This is in accordance with shell age deposition in the two assemblages, as differing from only 1000 years (see Table 3).

Characteristics of the molluscan assemblage of the modern lagoon

The modern malacological fauna of the lagoon as observed in 2022 (Table 2) is divided in two groups. The first group includes six species inhabiting “marite”, local name for oceanic water resurgences in the lagoon across the karstified atoll feo reliefs, only in a few points in the centre of the lagoon. We do not consider that this group of species is representative of the molluscan fauna in the whole lagoon. It includes four species already present in the Plio-Pleistocene units of Niau: Notocochlis ‌gualteriana ‌(Récluz, 1844), Gibberulus ‌gibbosus ‌(Röding, 1798), Longchaeus ‌maculosus ‌(Lamarck, 1822), Fragum ‌fragum ‌(Linnaeus, 1758) and Quidnipagus ‌palatam ‌Iredale, 1929. The material collected in 2008 and 2022 also includes a very few Melanoides ‌tuberculata ‌(O. F. Müller, 1774). We consider that they came from swamps which are their habitat and not the lagoon. Small fragments of Pinctada ‌maculata individuals (Gould, 1850) are observed in shore deposits, but it was possible to find alive some specimens in the lagoon.

The second group relates to three very abundant species inhabiting within the lagoon: Ctena ‌bella ‌(Conrad, 1837), Cerithium ‌punctatum ‌Bruguière, 1792 and Clypeomorus ‌brevis ‌(Quoy & Gaimard, 1834) as observed in 2022. But the assemblage observed in 2008 was different (Salvat et al. 2018) with only Ctena ‌bella and Cerithium ‌punctatum. Clypeomorus ‌brevis has been introduced to Niau during the last decade, and in 2022 the expansion of this gastropod in the lagoon proved to have been rapid that skeletal deposits on the edge of the lagoon are mainly composed of their dead shells. Further evidence of this introduction of Clypeomorus ‌brevis is provided by the shell necklaces and other decorative ornements that the inhabitants make to decorate their houses or to crown passing visitors when they leave. The necklaces worn by Niau inhabitants formerly included almost exclusively Ctena ‌bella valves, without any Clypeomorus ‌brevis or Cerithium ‌punctatum the last one being too small to be threaded. By contrast, the necklaces offered to visitors in 2022 consisted mainly of Clypeomorus shells.

The current characteristic fauna of the Niau lagoon therefore is limited to three species. This assemblage is typically less rich than that of the Mid-Late Holocene one and older ones. Ctena ‌bella is present in the Niau lagoon since the Late ‌Pliocene in the molluscan assemblage collected beneath the caliche crust in amazing abundance. This bivalve is also quantitatively dominant in all other assemblages until the modern times, including the sedimentary deposits overlying the caliche (dated at 3000-4000 years BP), the ancient cultivation taro pits (dated at around 2000 years BP) and the modern lagoon. Ctena ‌bella has probably been a permanent species living in the lagoon and its surrounding zones for more than three million years during higher sea stands, and may have survived in specific refuge zones during lower sea stands. Contrary to Ctena ‌bella, Cerithium ‌niauense ‌Merle, inhabiting the Niau lagoon from the Late ‌Pliocene to the Late ‌Holocene has disappeared. Cerithium ‌punctatum, already present in the Late ‌Pliocene assemblage but not very abundant, is absent in the Mid-Late Holocene deposits but present and abundant in the modern lagoon. Clypeomorus ‌brevis was introduced in the last decade. It is noteworthy that the three species widely colonizing the Niau lagoon tolerate significant variations in salinity and temperature. The inflow of ocean water during cyclones considerably changes the physico-chemical characteristics of the lagoon waters, especially if occurring after a long period of heavy rainfall or of strong evaporation. It is undoubtedly that Ctena ‌bella and Cerithium ‌punctatum owe their prosperity to their euryhaline and eurythermal capacities in the lagoon since more than 3 million years. The recent extinction of Cerithium ‌niauense ‌Merle, , which appears to have had the same geological history and the same ecological requirements at Niau as Ctena ‌bella and Cerithium ‌punctatum, seems difficult to explain. However, Ctena ‌bella and Cerithium ‌punctatum have a wider geographical distribution, which suggests a greater likelihood of adaptation to local environmental changes. Cerithium ‌niauense ‌Merle, , on the other hand, was endemic and therefore appeared to be at greater risk of extinction.

CONCLUSION

The uplifted atoll of Niau is a rather unique example in the central South Pacific, as it allows us to trace the response of malacological assemblages to environmental changes from the Late ‌Pliocene to the present day, in a well constrained temporal context. This work documents, in particular, the faunal extinctions observed during the Holocene, which are largely the result of the restriction of exchange with the open sea and the closure of the lagoon, in response to the uplift of the atoll. Thus, the Plio-Pleistocene assemblage, rich in more than 90 species, was replaced in the Mid and Late ‌Holocene by very impoverished assemblages with a species richness of no more than ten. Species endemic to the Plio-Pleistocene of the Niau Atoll account for 10% of the total malacological assemblage. They have been particularly hard hit by extinctions, with only species, Cerithium ‌niauense ‌Merle ‌n. sp., surviving from the Holocene. Future studies should be focused on comparison of the faunal composition between Niau and other Pacific atolls. Moreover, the deep origin of Pliocene faunas in Polynesia is also poorly known. The Makatea atoll, of Early Miocene age (Montaggioni et al. 1985), contains the oldest known malacofauna from French Polynesia, but it has been little studied and is known only from a list of a few taxa.

Acknowledgements

Warm thanks are given to Anton Eisenhauer, University of Frankfurt for providing dating results in 2013; to René Galzin and Magali Verducci for releasing ecological information about the Niau lagoon in 2010; to Michel Pichon for identifying the coral the species Leptoria ‌phrygia ‌(Ellis & Solander, 1786); to the “Department Environment, Culture et Patrimoine” of the French Polynesian Government for giving authorization to prospect on Niau Atoll in September-October 2022 as part of an archaeological mission organized and financially supported by the “Centre International de Recherche Archéologique de Polynésie” – incentive action led by Eric Conte, “Maison des Sciences de l’Homme”, “Université de la Polynésie française”; to Guillaume Molle and Vahine Rurua, archaeologists, for much appreciated collaboration in the field as well as Rodolphe Tehaamaru known as “Steven” and Heimaura Tiho known as “Tiho”; to the local authorities and the population of Niau for their kind welcome; to colleagues Nicolas Puillandre (MNHN) for loan of conids, Loïc Limpelaer for the the loan of Cerithium ‌tenellum, ‌Jean-Pierre Pointier (EPHE) for some figures, Eric Brunaud for his help in drawing graphics, Lilian Cazes and Philippe Loubry (MNHN/CNRS) for the photos of shells under natural light and under UV light, Blanchard Bouchard (MNHN) from reconstructing some brocken bivalves and Alexandre Lethiers for the infography. This paper benefited from the reviews of Jean-Jacques Cornée (Géosciences, Montpellier) and Jean-Paul Saint Martin (MNHN).

Fig. 1. — Geographic location of Niau Atoll (Tuamotu, French Polynesia) with local toponymy of sampling sectors. 10.5281/zenodo.19392531

Fig. 2. — Niau Atoll (Tuamotu, French Polynesia): A, aerial view of the northern part. In the foreground from left to right: village of Tupana, airplane runway and Ofare-Vaiohua sector; B, Coastline: fringing reef, conglomerate platform and beach, Ofare sector. Credit: A, P. Bacchet; B, B. Salvat.10.5281/zenodo.19384206

Fig. 3. — Niau Atoll (Tuamotu, French Polynesia): A, North-western rim side showing the Upper Pleistocene reef (last interglacial high sea stage) bordering the coast, South Ofare (Teruahina) sector; B, Southern reef-rim side, Mid Holocene algal crest, Phare sector. Credit: A, B. Salvat. 10.5281/zenodo.19392533

Fig. 4. — Niau Atoll (Tuamotu, French Polynesia): A, Cliff north of the atoll, airport area, showing the Mid-Upper Pleistocene reef unit; B, central part of the reef rim, Plio-Pleistocene feo zone, Vaiohua sector. Credit: B. Salvat.10.5281/zenodo.19384210

Fig. 5. — Niau Atoll (Tuamotu, French Polynesia): A, Southern reef-rim side, Pliocene reef remnants, Dragon sector, Niau Atoll (Tuamotu, French Polynesia); B, Cladium ‌mariscum-rich swamp with caliche patches, Vaiohua sector; C, caliche with an incorporated coral colony, Vaiohua sector. Credit: B. Salvat.10.5281/zenodo.19384215

Fig. 6. — Google Earth view of the Ofare-Vaiohua sector, northwest of Niau Atoll (Tuamotu, French Polynesia). Delineation of the different geomorphological units from the ocean to the lagoon with the location of the main mollusc collecting points. A, “Piscine” sector, Plio-Pleistocene thanatocenosis dredged from swamps; B, Vaiohua archeological platform, Late ‌Holocene thanatocenosis; C, coconut grove with Late ‌Holocene thanatocenosis (taro pit); D, lagoon, modern assemblage. 10.5281/zenodo.19392537

Fig. 7. — Topographical profile and morphological units of the Vaiohua sector from the ocean to the lagoon, Niau Atoll (Tuamotu, French Polynesia).10.5281/zenodo.19384220

Fig. 8. — Topographic profile of the Ofare-Vaiohua sector, northwest sector of Niau Atoll (Tuamotu, French Polynesia) with mollusk assemblages: 1, Plio-Pleistocene; 2, Holocene beds overlying the caliche; 3, Holocene deposits accessible from taro culture pits; 4, Modern lagoon. Caliche in red. ­­The assumption is made that the level of the lagoon is the same as that 0 m of the ocean.10.5281/zenodo.19384225

Fig. 9. — Species assemblage of Late ‌Holocene sediments deposited above the caliche (sample N105, Vaihuoa, near Archeological platform), Niau Atoll (Tuamotu, French Polynesia): A-C, Cerithium ‌columna ‌G. B. Sowerby I, 1834; A, MNHN.F.A98459; B, MNHN.F.A98460; C, MNHN.F.A98461; D-F, Cerithium ‌niauense ‌Merle ‌n. sp.,: D, MNHN.F.A98411; E, MNHN.F.A98412; F, MNHN.F.A98413; G-I, Cerithium ‌rostratum ‌G. B. Sowerby II, 1855: G, MNHN.F.A98462; H, MNHN.F.A98463; I, MNHN.F.A98464; J-L, Gafrarium ‌pectinatum ‌(Linnaeus, 1758): J, MNHN.F.C02086; K, MNHN.F.C02087; L, MNHN.F.C02088; M-O, Fragum ‌fragum ‌(Linnaeus, 1758): M, MNHN.F.C02089; N, MNHN.F.C02090; O, MNHN.F.C02091; P-R, Ctena ‌bella ‌(Conrad, 1837): P, MNHN.F.C02092; Q, MNHN.F.C02093; R, MNHN.F.C02094. Scale bars: 10 mm. Credit: J.-P. Pointier.10.5281/zenodo.19384229

Fig. 10. — Assemblage of the four common species living in the lagoon (sample N95, Vaihuoa, lagoon shore), Niau Atoll (Tuamotu, French Polynesia): A-C, Clypeomorus ‌brevis ‌(Quoy & Gaimard, 1834): A, MNHN.F.C02095; B, MNHN.F.C02096; C, MNHN.F.C02097; D-G, Cerithium ‌punctatum ‌Bruguière, 1792: D, MNHN.F.C02098; E, MNHN.F.C02099; F, MNHN.F.C02100; G, MNHN.F.C02101; H-J, Ctena ‌bella ‌(Conrad, 1837): H, MNHN.F.C02102; I, MNHN.F.C02103; J, MNHN.F.C02104; K-M, Pinctada ‌maculata ‌(A. Gould, 1850): K, MNHN.F.C02105; L, MNHN.F.C02106; M, MNHN.F.C02107. Ctena ‌bella is the dominant bivalve with Clypeomorus ‌brevis. Scale bar: 10 mm. Credit: J.-P. Pointier.10.5281/zenodo.19384232

Fig. 11. — Cerithium ‌niauense ‌Merle ‌n. sp., from the Plio-Pleistocene (A-F) and the Late ‌Holocene at Vaihuoa near archeological platform (G-V) of Niau Atoll (Tuamotu, French Polynesia): A, holotype, MNHN.F.A98401, ventral face; B, idem in ventral face under UV light; C, idem, dorsal face; D, paratype MNHN.F.A98402, ventral face; E, idem, dorsal face, F, idem, dorsal face under UV light; G-H, paratype (sample N106), MNHN.F.A98404, ventral (G) and dorsal (H) faces; I, J, paratype (sample N106), MNHN.F.A98405, ventral (I) and dorsal (J) faces; K, L, paratype (sample N108), MNHN.F.A98403, ventral (K) and dorsal (L) faces; M, N, paratype (sample TP1A), MNHN.F.A98406, ventral (M) dorsal (N) faces; O, P, paratype (sample TP1A), MNHN.F.A98407, ventral (O) and dorsal (P) faces; Q, R, paratype (sample TP1B), MNHN.F.A98408, ventral (Q) and dorsal (R) faces; S, T, paratype (samples TP1B), MNHN.F.A98409, ventral (S) and dorsal (T) faces; U, V, paratype (sample TP1B), MNHN.F.A98410, ventral (U) and dorsal (V) faces; W, X, Cerithium ‌tenellum ‌G. Sowerby II, 1855 (Limpelaer coll.), Pelotes Point, Philippines, present day, ventral (X) and dorsal (Y) faces for comparison with C. ‌niauense ‌Merle ‌n. sp., Scale bars: 5 mm. Credits: A-F, P. Loubry; G-Y, L. Cazes. B and F, photos taken under UV, other photos taken in natural light. A-F, M-V, material from Letourneux coll.; G-L, material from Salvat coll. 10.5281/zenodo.19392543

Fig. 12. — Strombidae (A-D) and Muricidae (E-G) from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A, B, Gibberulus ‌gibbosus ‌(Röding, 1798), MNHN.F.A98429: A, ventral face under UV light; B, dorsal face under UV light; C, D, Striatostrombus ‌blanci ‌(Tröndlé & Salvat, 2010), MNHN.F.A98432: C, ventral face in natural light; D, ventral face under UV light; E-G, Drupella ‌margariticola ‌(Broderip, 1833): E, F, MNHN.F.A98434, ventral and dorsal faces under UV light; G, MNHN.F.A98435, ventral face under UV light. Scale bars: 10 mm. Credits P. Loubry (MNHN/CNRS). All material from Letourneux coll. housed at MNHN.10.5281/zenodo.19384237

Fig. 13. — Conus(Conus)letourneuxi ‌Merle ‌n. sp., (A-D) and Conus(Tesselliconus)georgesrichardi ‌Merle ‌n. sp., (E-Q) from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A-D, holotype, MNHN.F.A98436 (Letourneux coll.), ventral (A) and dorsal (B) faces in natural light, profil view under UV light (C) and in inverse UV light (D); E-H, holotype, MNHN.F.A98437, ventral face in natural light (E) and under UV light (F), dorsal face in natural light (G) and under UV light (H); I, J, paratype, MNHN.F.A98438, ventral (I) and dorsal (J) faces under UV light; K, paratype, MNHN.F.A98439, broken specimen in ventral face under UV light; L-O, paratype, MNHN.F.A98440, ventral face in natural light (L) and under UV light (M), dorsal face in natural light (N) and under UV light (O); P-Q, paratype, MNHN.F.A98441, ventral (P) and dorsal (Q) faces under UV light. Scale bars: A-D, K, 20 mm; E-J, L-Q, 10 mm. Credits: A, B, E, F, L-N, L. Cazes (MNHN/CNRS); C, D, F, H, I, J, K-M, O, P. Loubry (MNHN/CNRS). All material from Letourneux coll. housed at MNHN.10.5281/zenodo.19384244

Fig. 14. — Conus(Tesselliconus)georgesrichardi ‌Merle ‌n. sp., (A-L) and Oxymeris ‌niauensis ‌(Tröndlé & Letourneux, 2011) (M-P) from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A, B, paratype, MNHN.F.A98442, ventral (A) and dorsal (B) faces under UV light; C, paratype, MNHN.F.A98443, ventral face under UV light; D, E, paratype, MNHN.F.A98444, ventral (D) and dorsal (E) faces under UV light; F, G, paratype, MNHN.F.A98445, ventral face under UV light (F) and in inverse UV light (G); H, I, paratype, MNHN.F.A98446, ventral (H) and dorsal (I) faces under UV light; J-L, paratype, MNHN.F.A98448 dorsal face under UV light (J) and ventral face in natural light (K) and under UV light (L); M-P, paratype, Letourneux coll., ventral face in natural light (M) and under UV light (N) and dorsal face in natural light (O) and under UV light (P). Scale bars: A-M, 10 mm; N-P, 20 mm. Credits: P. Loubry (MNHN/CNRS). A-L, material from Letourneux coll. housed at MNHN; M-O, material from Letourneux coll., at Tahiti.10.5281/zenodo.19384251

Fig. 15. — The fourth areas (a, b, c, d) of pigmentation in Conus(Tesselliconus)georgesrichardi ‌Merle ‌n. sp., (A-D), Conus(Tesselliconus)tessulatus ‌Born, 1778 (E, F) and Conus(Tesselliconus)eburneus ‌Hwas, 1792 (G, H): A, B, holotype, MNHN.F.A98437 (Letourneux coll.), ventral face (A) and dorsal (B) faces under UV light, Plio-Pleistocene, Niau Atoll (Tuamotu, French Polynesia); C, D, paratype, MNHN.F.A98446 (Letourneux coll.), ventral (C) and dorsal (C) faces under UV light, Plio-Pleistocene, same locality; E, F, MNHN.IM (Tröndlé coll.), ventral (E) and dorsal faces (F), present day, Papeete (Faaone), Tahiti island (Tuamotu, French Polynesia); G, H, MNHN.IM (Pierrot coll.), ventral (G) and dorsal faces (H), present day, Tahiti island. Scale bars: 20 mm. Credits: P. Loubry (MNHN/CNRS).10.5281/zenodo.19384255

Fig. 16. — Bulla ‌niauensis ‌Merle ‌n. sp., from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A-E, holotype, MNHN.F.A98450 (Letourneux coll.), ventral face in natural light (A) and under UV light (B), dorsal face in natural light (C), under UV light (D) and in inverse UV light (E); paratype, MNHN.F.A98451 (Letourneux coll.), profil view under UV light (F) and in inverse UV light (G). Scale bars: 10 mm. Credits: P. Loubry (MNHN/CNRS).10.5281/zenodo.19384259

Fig. 17. — ?Lunulicardia ‌deformata ‌Merle ‌n. sp., from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A, B, holotype, MNHN.F.A99068, right valve, internal (A) and external viewes (B); C, paratype, MNHN.F.A99822, left valve, internal view; D, paratype, MNHN.FA99823, left valve, external view; E, F, paratype, MNHN.A.99821, external (E) and internal (F) views; G, enlarged view of the hinge ot the holotype; H, enlarged view of the hinge of the paratype MNHN.F.A99822. Scale bars: A-F, 10 mm, G, H, 5 mm. Credits: P. Loubry. Material from Letourneux coll. housed at MNHN.10.5281/zenodo.19384262

Fig. 18. — Tellinidae (A-L) from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A-C, Tellinellacf.virgata ‌(Linnaeus, 1758), MNHN.F.A98454, left valve, internal view in natural light (A), external view in natural light (B) and under UV light (C); D, E, Tellinella ‌virgata ‌(Linnaeus, 1758) for comparison, MNHN.F.C02108 (Salvat coll.), present day, Rurutu island (Tuamotu, French Polynesia), left valve (D) and right valve (E); F-L, Indotellina ‌fakaauensis ‌Merle ‌n. sp.,; F-I, holotype MNHN.F.A99067, external view of the right valve (F), external view of the left valve (G), view of the posterior margin (H), view of the ventral margin (I); J, K, paratype MNHN.F.A99069, internal view of the right valve (J), internal view of the left valve (K); L, paratype MNHN.F.A99824, external view of the right valve. Scale bars: 10 mm. Credits: A-C, F-L, P. Loubry (MNHN/CNRS); D-E, L. Cazes (MNHN/CNRS). A-C, F-L, material from Letourneux coll. housed at MNHN.10.5281/zenodo.19384267

Fig. 19. — ?Gafrarium ‌troendlei ‌Merle ‌n. sp., from the Plio-Pleistocene assemblage of Niau Atoll (Tuamotu, French Polynesia): A-D, holotype, MNHN.F.A98456, left valve, internal view in natural light (A), external view in natural light (B), under UV light (C) and in inverse UV light (D); E, F, paratype, MNHN.F.A98457, right valve, internal view (E) and external view (F) in natural light. Scale bars: 10 mm. Credits: A-C, P. Loubry (MNHN/CNRS); E, F, L. Cazes (MNHN/CNRS). Material from Letourneux coll. housed at MNHN.10.5281/zenodo.19384274

Table 1. — Assemblage of the 92 molluscan species identified at specific rank from the Plio-Pleistocene of Niau Atoll (Tuamotu, French Polynesia). Abundances: A, from 1 to 5 shells or valves; B, between 6 and 20; C, between 21 and 100; D, more than 100. Substrates: S, sandy; H, hard. Distribution: IP, Indo-Pacific; WP, West Pacific; P, Pacific. ▲, Endemic and extinct species (bold); , species only extinct in French Polynesia. 16A475DFC222FFB5FF25FF44FBDEFE98 Families Species Abundances Substrates Distributions Scissurellidae Scissurella ‌mirifica ‌(A. Adams, 1862) A H WP Skeneidae Lodderena ‌emeryi ‌(Ladd, 1966) A H WP Turbinidae Astralium ‌confragosum ‌(Gould, 1851) A H P Turbo ‌fakaauensis Tröndlé & Letourneux, 2012 ▲ A H Endemic Tornidae Lophocochlias ‌parvissimus ‌(Hedley, 1899) A H IP Neritidae Nerita ‌chamaeleon Linnaeus, 1758  C H IP Nerita ‌plicata Linnaeus, 1758 B H IP Nerita ‌histrio ‌Linnaeus, 1758 B H IP Cerithiidae Cerithium ‌columna ‌Sowerby I, 1834 B S IP Cerithium ‌echinatum ‌Lamarck, 1822 B S IP Cerithium ‌nodulosum ‌Bruguière, 1792  A S IP Cerithium ‌punctatum ‌Bruguière, 1792 D S IP Cerithium ‌rostratum ‌G.B. Sowerby II, 1855 C S IP Cerithium niauense Merle, n. sp. ▲ D S Endemic Cerithium ‌zebrum ‌Kiener, 1841 C H IP Clypeomorus ‌bifasciata ‌(G.B. Sowerby II, 1855)  D H IP Rhinoclavis ‌aspera ‌(Linnaeus, 1758) A S IP Modulidae Indomodulus ‌tectum ‌(Gmelin, 1791) A H IP Planaxidae Hinea ‌fasciata ‌(Pease, 1868) A H IP Scaliolidae Finella ‌pupoides ‌A. Adams, 1860 D S IP Littorinidae Littoraria ‌coccinea ‌(Gmelin, 1791) A H IP Peasiella ‌conoidalis ‌(Pease, 1868) A H IP Naticidae Notocochlis ‌gualteriana ‌(Récluz, 1844) C S IP Polinices ‌mammilla ‌(Linnaeus, 1758) C S IP Barleeidae Protobarleeia ‌myersi ‌(Ladd, 1966)  B H WP Rissoinidae Apataxia ‌cerithiiformis ‌(Tryon, 1887) A H IP Zebinidae Zebinella ‌tenuistriata ‌(Pease, 1868) A H IP Rissoina ‌oryza ‌Garrett, 1873  A H WP Truncatellidae Taheitia ‌scalariformis ‌(Reeve, 1842) C S WP Cypraeidae Lyncina ‌propinqua ‌(Garrett, 1879) A H IP Mauritia ‌maculifera ‌Schilder, 1932 A H IP Mauritia ‌scurra ‌(Gmelin, 1791) A H IP Monetaria ‌moneta ‌(Linnaeus, 1758) C H IP Naria ‌erosa ‌(Linnaeus, 1758) C H IP Strombidae Canarium ‌mutabile ‌(Swainson, 1821) A S IP Gibberulus ‌gibbosus ‌(Röding, 1798) C S IP Striatotrombus ‌blanci (Tröndlé & Salvat, 2010) ▲ C S Endemic Cymatiidae Gutturnium ‌muricinum ‌(Röding, 1798) B H IP Tonnidae Malea ‌pomum ‌(Linnaeus, 1758) A H IP Columbellidae Euplica ‌borealis ‌(Pilsbry, 1904)  B H WP Nassariidae Nassarius ‌bellulus ‌(A. Adams, 1852)  A S IP Nassarius ‌papillosus ‌(Linnaeus, 1758) A S IP Muricidae Drupella ‌margariticola ‌(Broderip, 1833) B H IP Mitridae Strigatella ‌litterata ‌(Lamarck, 1811) A H IP Carinomitra ‌saltata ‌(Pease, 1865) A H WP Conidae Conus ‌catus ‌Hwass in Bruguière, 1792 A H IP Conus letourneuxi Merle, n. sp. ▲ A H Endemic Conus georgesrichardi Merle, n. sp. ▲ C H Endemic Terebridae Oxymeris ‌niauensis (Tröndlé & Letourneux, 2011) ▲ B S Endemic Acteonidae Pupa ‌sulcata ‌(Gmelin, 1791) C S IP Pyramidellidae Parthenina ‌cossmanni ‌(Hornung & Mermod, 1924) A S IP Herviera ‌gliriella ‌(Melvill & Standen, 1896) A S IP Miralda ‌scopulorum ‌(Watson, 1886) A S WP Odostomia ‌sperabilis ‌Hedley, 1909 B S WP Otopleura ‌mitralis ‌(A. Adams, 1854) A S IP Otopleura ‌nitida ‌(A. Adams, 1854) A S IP Pyramidellidae (continuation) Longchaeus ‌maculosus ‌(Lamarck, 1822) A S IP Pyrgulina ‌pupaeformis ‌(Souverbie, 1865) A S IP Turbonilla ‌mumia ‌(A. Adams, 1861) A S IP Bullidae Bulla niauensis Merle, n. sp. ▲ B S Endemic Tornatinidae Acteocina ‌sandwicensis ‌Pease, 1860 C S WP Ellobiidae Allochroa ‌layardi (H. & A. Adams, 1855) A H IP Melampus ‌castaneus ‌(Muehlfeldt, 1818) A H IP Microtralia ‌alba ‌(Gassies, 1865)  A H WP Microtralia ‌lucida ‌(Pease, 1869) A H WP Mytilidae Modiolus ‌auriculatus ‌(Krauss, 1848) B H IP Musculus ‌viridulus ‌(H. Adams, 1871) A H IP Arcidae Acar ‌congenita (E.A. Smith, 1885) A S IP Anadara ‌oceanica ‌(Lesson, 1831) A S IP Barbatia ‌foliata (Forsskal in Niebuhr, 1775) A H IP Philobryidae Cratis ‌kanekoi ‌Hayami & Kase, 1993 A S WP Vulsellidae Electroma ‌alacorvi ‌(Dillwyn, 1817)  A H IP Ostreidae Dendostrea ‌sandvichensis ‌(G.B. Sowerby II, 1871) A H IP Gryphaeidae Hyotissa ‌numisma ‌(Lamarck, 1819) A H IP Margaritidae Pinctada ‌maculata ‌(Gould, 1850) B H IP Cardiidae Fragum ‌fragum ‌(Linnaeus, 1758) D S IP ?Lunulicardia deformata Merle, n. sp. ▲ B S Endemic Tridacna ‌maxima ‌(Röding, 1798) A H IP Tellinidae Jactellina ‌clathrata ‌(Deshayes, 1835) B S IP Pinguitellina ‌robusta ‌(Hanley, 1844) A S IP Cadella ‌crebrimaculata ‌(G.B. Sowerby II, 1868) A S WP Scissulina ‌dispar ‌(Conrad, 1837) C S IP Scutarcopagia ‌scobinata ‌(Linnaeus, 1758) A S IP Quidnipagus ‌palatam ‌Iredale, 1929 B S IP Tellinella cf. virgata ‌(Linnaeus, 1758) A S ?IP Indotellina fakaauensis Merle, n. sp. ▲ B S Endemic Tonganaella ‌perna ‌(Spengler, 1798) A S IP Chamidae Chama ‌limbula ‌Lamarck, 1819 A H IP Lucinidae Codakia ‌punctata ‌(Linnaeus, 1758) B S IP Ctena ‌bella ‌(Conrad, 1837) B S IP Veneridae Gafrarium ‌pectinatum ‌(Linnaeus, 1758) C S IP ?Gafrarium troendlei Merle, n. sp. ▲ B S Endemic Table 2. — Assemblages of molluscan species from the Mid Holocene (Aturona), Late ‌Holocene (Vaiohua, archeological platform), Late ‌Holocene (Vaiohua, taro pit) and modern lagoon of Niau Atoll (Tuamotu, French Polynesia). As a reminder, species already present in the Plio-Pleistocene are provided in the first column. m for species only present in “marite”. 16A475DFC220FFB7FF27FF44FE2CFE98 Families Species Plio-Pleistocene Mid Holocene (Aturona) Late ‌Holocene (Vaiohua archaeological platform) Late ‌Holocene (Vaiohua, taro pit) Modern Lagoon Cerithiidae Cerithium ‌columna ‌G.B. Sowerby I, 1834 × – × × m Cerithium ‌punctatum ‌Bruguière, 1792 × – – – × Cerithium ‌rostratum ‌G.B. Sowerby II, 1855 × – × – – Cerithium ‌niauense ‌Merle ‌n. sp., × × × × – Clypeomorus ‌brevis ‌(Quoy & Gaimard, 1834) – – – – × Thiaridae Melanoides ‌tuberculata ‌(O. F. Müller, 1774) × × – – – Naticidae Notocochlis ‌gualteriana ‌(Récluz, 1844) × – – – m Strombidae Gibberulus ‌gibbosus ‌(Röding, 1798) × – – – m Pyramidellidae Longchaeus ‌maculosus ‌(Lamarck, 1822) × – – – m Ostreidae Dendostrea ‌sandvichensis ‌(G. B. Sowerby II, 1871) × – × – – Margaritidae Pinctada ‌maculata ‌(Gould, 1850) × – – – × Cardiidae Fragum ‌fragum ‌(Linnaeus, 1758) × – × × m Tellinidae Quidnipagus ‌palatam ‌Iredale, 1929 × × – – m Tellinella ‌virgata ‌(Linnaeus, 1758) × × – – – Lucinidae Ctena ‌bella ‌(Conrad, 1837) × × × × × Veneridae Gafrarium ‌pectinatum ‌(Linnaeus, 1758) × × × – – Table 3. — Radiocarbon data: fraction of modern carbon (pMC), conventional ages and calibrated ages (Niau Atoll, French Polynesia). The ages obtained were calibrated with the IntCAL Marine 20 curve (Heaton et al. 2020) and the Oxcal4.4 software (Bronk Ramsey 2001). The reservoir age correction used was made with ΔR 140 ± 20 years based on data obtained for French Polynesia (Petchey et al. 2008). 16A475DFC220FFB7FF24FC7CFC9FFBA3 Sample numbers Labcodes Nature Locations mg C Delta C13 pMC Err pMC Ages in years Err age BP Calibrated age (years cal BP) Epoch N 57 71233 Quidnipagum ‌palatam Aturona 1.22 3.80 49.09739 0.16352 5715 30 6238-5912 Mid Holocene N 103 SAC -70407 Cerithium sp. Vaiohua 1.14 0.50 61.95487 0.17497 3845 30 3982-3627 Late ‌Holocene N 107 71234 Ctena ‌bella Vaiohua (Taro pit) 1.25 5.30 76.11125 0.21268 2195 30 1940-1610 Late ‌Holocene N 121 SAC -70408 Cerithium sp. Vaiohua 0.83 –1.40 66.39803 0.17884 3290 30 3310-2954 Late ‌Holocene