Remains of the digestive system in the middle Cambrian trilobite Ptychoparioides henkli Kordule, 2006 (Barrandian area, Czech Republic)

Preservation of the digestive system in trilobites is extremely rare: from the Barrandian area, such remains have been recorded in two Cambrian and eight Ordovician trilobite genera. In this contribution we describe eight new examples of articulated trilobites displaying remains of the digestive system in the axial parts of the cephalon and thorax from the middle Cambrian Buchava Formation of the Skryje-Týřovice Basin. All studied specimens are identified as Ptychoparioides henkli Kordule, 2006 and exhibit up to four pairs of cavities or light-coloured markings under the central and posterior parts of the glabella, one pair in the occipital ring and up to six pairs in the axis of the anterior thoracic segments. These cavities or light-coloured markings are interpreted as remains of metamerically paired digestive caeca of the «perigastric organ». An anteriorly rounded, posteriorly widely V-shaped body preserved in the frontal glabellar lobe of a conical glabella in one specimen most probably represents a remnant of the foregut chamber. These specimens constitute the first example of digestive structures observed in Cambrian ptychopariid trilobites in the Barrandian area. A dark-coloured axial surface preserved in eight thoracic segments between and behind paired cavities or markings is present in two specimens; this surface is interpreted as remains of the hindgut. The occurrence of trilobites preserving digestive-system remains together with locally abundant articulated echinoderms and ontogenetic stages of trilobites, as well as previously described bivalved arthropods, confirm that the depositional environment of the Buchava Formation was favourable for exceptional preservation of fossils, including soft-tissue preservation.