ENIGMATIC ECHINODERM: OLDEST POST-ORDOVICIAN MEMBER OF THE OPHIOCISTIOIDEA?

A possible ophiocistioid echinoderm is reported from Telychian (Llandovery, Silurian) strata (Cybèle Member, Jupiter Formation) of Anticosti Island, Québec, Canada. This fossil is preserved along the concave, inner surface of an orthocone cephalopod mold. It consists of a subcircular disc with a large eccentric pore and ten partial or complete, narrow appendages. The central disc is approximately 4 mm in diameter and the entire organism was as much as 30 mm in diameter. Faint remnants of apparent tessellate plating exist on the central disc and appendages. The style of plating, ten appendages, and a large eccentric pore on the aboral surface rule out clades other than the Ophiocistioidea.

If an ophiocistioid, the aboral surface of the theca is covered with small plates and has an eccentric periproct. It has ten plated tube feet (two per ray) that extend beyond the theca and are visible from an aboral view. Plates on the theca and tube feet meet primarily in triple junctions, which is characteristic for tessellate plating. The generic assignment of this specimen is unresolved at this time, but this putative ophiocistioid shares similarities with some members of the Eucladidae and Sollasinidaea. Anticosti Island strata record both Late Ordovician mass extinctions and the earliest Silurian recovery of benthic shelly faunas. If an ophiocistioid, this is the oldest, post-Late Ordovician extinction ophiocistioid known.