Notioceramus Fisher 1940

Notioceramus Fisher, 1940

Notioceramus Fisher, 1940: 119; Mah 2011: 32.

Diagnosis

Body stellate. Abactinal, marginal, and actinal surface densely covered by large, coarse, hemispherical granules that nearly obscure plate boundaries. Body wall thin, parchment like. Marginal plates with lateral facing. Furrow spines two to three, subambulacrals large.

Comments

The two new species of Notioceramus described here were collected from substantially deeper habitats than the type species, Notioceramus anomalus Fisher, 1940, which has been recorded primarily from 342–750 m (Fisher 1940; A.M. Clark 1962). In contrast, the new species described herein Notioceramus abyssalis n. sp. and Notioceramus neillae n. sp. were collected from abyssal depths (2324–3876 m).

A trend in the degree to which features were calcified was observed between the deepest and shallowest species. The deepest occurring individuals of Notioceramus abyssalis n. sp. showed more tapering arms, granules with spinose surfaces, fewer granules overall, more rough-tipped actinal spines, and more weakly developed abactinal and marginal plates. This contrasted with Notioceramus anomalus which showed greater numbers of perfectly spherical granules, more stout arms, and more strongly calcified abactinal and marginal plates. Notioceramus neillae n. sp. appeared intermediate between the two. However only two individuals of N. neillae n. sp. were available.

It is difficult to assess the polarity of these morphological trends without a full phylogenetic assessment of Notioceramus and its sister taxa and as such, difficult to conclude whether the derived species shows accentuated calcification or decalcification of the endoskeleton and its accessories. Based on affinities outlined below, both shallow and deep-water sister taxa are plausible making an assessment difficult without further information.