Evoplosoma Fisher 1906

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 42-43

Evoplosoma Fisher 1906

Fisher 1906: 1065; Koehler 1909: 96; Spencer & Wright 1966: U58; Clark & Downey 1992: 241; A.M. Clark 1993: 253; Mah et al., 2010: 278; Mah 2015a: 2.

Diagnosis (from Mah, 2015a). Body strongly stellate. Arm narrow, elongated. R/r ranges from 2.3–4.11 (most between 3.0–4.0). Interradial arcs straight to weakly curved.

Abactinal plates, flat and platform-like. Carinal series poorly distinguished. Abactinal plates tightly articulated. Body covered by tissue layer with pulpy texture that overlies plates and spines (seen more clearly in wet specimens). Prominent spines on abactinal, superomarginal, inferomarginal and actinal plates in most species. Spine morphology variable from blunt conical to pointed, to cylindrical or small and spinelet-like. Granules with spiny tips in most species, with some having rounded surfaces. Granules present but with variable abundance among species. Tonglike pedicellariae with serrated valves present or absent on abactinal, marginal or actinal surface.

Marginal plates generally quadrate in shape, some showing direct 1:1 superomarginal/inferomarginal correspondence but others being more offset. Marginals relatively numerous ranging in number from 30–70 per interradius. Some species with bare marginal plate surface, but most with even to dense granule covering. Granules varying from having rounded surface to pointed or prismatic edges. Large prominent spine or spines known in all but one species. Large single spines observed as a linear series in several species. Spinelets or multiple shorter spines observed on marginal plate surfaces of other species. Pedicellariae variably present on either supero or inferomarginal series.

Actinal intermediate regions relatively small with fewer than six rows present (three or four present in most species). Actinal plate boundaries obscured by pulpy tissue layer and/or granulation. Granules round or with spiny edges present on all species. Primary spines present on actinal plate surface in most species.

Furrow spines varying in number from 2–3, to 7–12. Spines generally compressed, quadrate to polygonal in cross section. Tips varying from smooth and blunt to jagged with furrowed tips. Subambulacral spination variable but a felipedal (clamp-like bivalve) pedicellariae present among the subambulacrals in most species. Subambulacrals varying but spination ranging from blunt spines, pointed spinelets to pointed or rounded granules.

Based on in situ observations herein and from prior accounts (e.g. Mah et al. 2010), the color of most species ranges from yellow to deep orange.

Comments. Evoplosoma is a genus of nine species, including five in the Pacific, three Atlantic and a single species from the Indian Ocean, all from deep-sea settings (approximately 750–2600m). Although described from the early 20th Century ( Fisher 1906) the ecology of these species, including their role as deep-sea corallivores preying upon octocorals, particularly those in the Isididae , had only become known more recently as deep-sea video has become more widespread ( Mah et al. 2010; Mah 2015a). Evoplosoma and Hippasteria are both members of the Hippasterinae , a subfamily within the Goniasteridae . Although all species within these genera have yet to have been identified as corallivores most observations have shown them to be predators of either octocorals or other colonial cnidarians, such as antipatharians.

Evoplosoma was identified based on the presence of its elongate, triangular arms, the sharp, conical spines present on the marginal plates, and the pulpy granular surface. Two species were identified, Evoplosoma forcipifera , which was originally described from the Hawaiian Islands and a newly discovered species, Evoplosoma nuku n. sp. Both species were observed feeding on colonial octocorals.