Degeneraster spenceri n. gen., n. sp. (Asteroidea; Ordovician) and interpretating the early history of the Asterozoa

Degeneraster spenceri n. gen., n. sp., a new genus and species of Asteroidea de Blainville, 1830 (­Echinodermata) from the Late Ordovician (middle Katian) of Morocco, is described. Similarities and differences between basal Somasteroidea Spencer, 1951 and D. spenceri n. gen., n. sp. are reviewed. Based on ambulacral (i.e., axial and adaxial) morphology, D. spenceri n. gen., n. sp. is assigned to the basal asteroid order Euaxosida Blake, 2018; extraxial morphology in contrast includes expressions that are widely found among more derived Paleozoic asterozoans. Degeneraster spenceri n. gen., n. sp. is anomalous among euaxosidan Asteroidea in lacking an ambital framework. In addition, the aboral skeleton is distinctive, and podial pores, otherwise undocumented among euaxosidans, might occur. Atypical expressions provide basis for the recognition of the new family Degenerasteridae n. fam. Differences among D. spenceri n. gen., n. sp., other Euaxosida, and the derived asteroid Paleozoic orders Hadrosida and Kermasida are surveyed. To exemplify early asterozoan diversity, the ophiuroid Componaster Glass, Blake & Lefebvre, 2024 and unassigned Falloaster Blake, Gahn & Guensburg, 2020a, are cited and ­illustrated for comparison with D. spenceri n. gen., n. sp. and other early Asterozoa.