An archegonaster-like somasteroid (echinodermata) from pomeroy, co. tyrone, Northern Ireland

Catervaparmaster pecularis n. gen. and sp. (Somasteroidea; Echinodermata) is described from the Caradoc and Shermanian (Ordovician) of Ireland. Although the single known specimen is incomplete and poorly preserved, it is unique among stelleroids (Somasteroidea, Asteroidea and Ophiuroidea) in lacking adambulacral (=lateral) ossicles. Different phylogenetic interpretations are possible, but based on similarities between Archegonaster and Catervaparmaster the absence of adambulacrals appears secondary (autapomorphic) and therefore phylogenetically of limited significance. Adambulacrals serve key structural functions in recent stelleroids; their absence from Catervaparmaster suggests that adambulacral function was not firmly fixed at this point in stelleroid history.