Durhamicystis, Zamora, Sprinkle & Sumrall, 2020

Zamora, Samuel, Sprinkle, James & Sumrall, Colin D., 2020, A revaluation of rhipidocystid echinoderms based on a new flattened blastozoan from the Upper Ordovician of Maryland, USA, Acta Palaeontologica Polonica 65 (3), pp. 455-465 : 457

Genus Durhamicystis nov.

Zoobank LSID: urn:lsid:zoobank.org:act:D0CB18AA-6423-4615-B331-18A8A3C28B36

Type species: Durhamicystis americana sp. nov.; by monotypy, see below.

Etymology: In honour of the paleontological specialist on echinoids and Cambrian echinoderms, John Wyatt Durham (University of California, Berkeley) who examined these specimens while visiting the Smithsonian in 1966–1967, and arranged for their eventual donation.

Diagnosis.—As for the type species by monotypy.

Remarks.— Durhamicystis is assigned to the family Rhipidocystidae based on the elongate and flattened theca, brachioles on both sides of the oral area, and marginal plates. The original description and illustration of Rhipidocystis baltica (type species of the genus) by Jaekel (1901) was very limited including a single drawing that shows an echinoderm with large marginal plates, centrals, and stem facet. The genus was reviewed by Ubaghs (1968) for his chapter on eocrinoids for the Treatise, who figured additional material assigned to Rhipidocystis that was bilaterally symmetrical and showed only two ambulacra with flattening on the A-CD plane. Rozhnov (1989) was first to reconstruct Rhipidocystis in detail showing an animal with a flattened theca and flattening along the BC-DE plane. He also moved the material showing bilateral symmetry described by Ubaghs (1968) to the genus Neorhipidocystis , that also included R. norvegica ( Bockelie, 1981) described from a different part of Baltica. The new material described herein is very similar to Neorhipidocystis in the shape of the theca, oral area, split marginal above the periproct, and flattening pattern. If previous observations are correct, then Rhipidocystis includes forms with a very different flattening pattern, and thus the family status should be reconsidered (see discussion below).