A new brittle star (Echinodermata: Ophiuroidea) from the uppermost Cretaceous of Wakayama Prefecture, Japan provides insights into deep-sea colonization by the extant family Ophiosphalmidae

Abstract

Well-preserved external molds of an articulated brittle star from the upper lower Maastrichtian (Upper Cretaceous) strata of the Futakawa Formation (Sotoizumi Group) of Wakayama, southwestern Japan, are described as a new ophiosphalmid genus and species, Enakosphalma nagashimai. It differs from other members of the Ophiosphalmidae in having lateral arm plates with a smooth outer surface stereom, a beveled outer proximal edge, very small spine articulations grouped ventrally in a shallow depression, small dorsal and ventral contact surfaces with the opposite lateral arm plates, oval radial shields, small disc scales, a large oval plate in the ventral interradius, small and rounded pentagonal oral shields, and tentacle pores developed as between-plate openings until the sixth arm segment. The new species is morphologically intermediate between Enakomusium from the Jurassic of Europe and the extant Ophiosphalma. It therefore contributes to a better understanding of the fossil record and evolutionary history of the important deep-sea family Ophiosphalmidae. It furthermore demonstrates that the Ophiosphalmidae have inhabited deep-sea environments since at least the Late Cretaceous.

ZooBank registration: urn:lsid:zoobank.org:pub:58D441C1-ACCA-464C-BABF-A766BFE2096D