Evoplosoma Fisher 1906

Mah, Christopher L., 2024, New genera and species of deep-sea Goniasteridae (Asteroidea) from the North Pacific, Zootaxa 5543 (4), pp. 451-500 : 472-473

Evoplosoma Fisher 1906

Evoplosoma 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 2015 b: 2; 2022: 42

Diagnosis (from Mah, 2015 b).

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 thick, rough 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 s pecies, with some having rounded surfaces. Granules present but with variable abundance among species. Tong-like pedicellariae with serrated valves present or absent on abactinal, marginal or actinal surface, variably present on super or inferomarginal plate series. Marginal plates generally quadrate in shape, some showing direct 1:1 superomarginal/inferomarginal correspondence but others being more offset. Marginals 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. 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 on all species. Primary spines on actinal plate surface in most species. Furrow spines varying in number from 2–3, to 7–12 but generally high. Spines generally compressed, quadrate to polygonal in cross section. Tips varying from smooth and blunt to jagged with furrowed tips. Felipedal (clamp-like bivalve) pedicellariae present among the subambulacrals in most species. Subambulacrals variable with 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 includes 14 species found in the Atlantic, Indian and Pacific oceans and occurring primarily between 1000 and 3000 m depth. Evopolosma was reviewed by Mah (2015) and later augmented ( Mah 2020, 2022, 2024). Definitions of most species show distinct diagnostic characters, but many are present at inaccessible sampling depths, which often precludes sufficient specimen samples that would permits a conventional assessment of morphological variation. An assessment of Evoplosoma spp. is in preparation.

Relatively few species are known from more than one individual, but those that do are apparently widely occurring (e.g Mah 2024). Evoplosoma timorensis Aziz & Jangoux 1985 , for example, has been reported from throughout the Central and South Pacific and the Indian Oceans and although only two specimens of Evoplosoma voratus have been recorded, occurrence suggests a presumptive range between the North Pacific, off Davidson Seamount and Ningaloo Canyon off the coast of Western Australia in the Indian Ocean (Mah, 2024).

Evoplosoma and other related taxa in the Hippasterinae have found increasing ecological relevance as submersibles have observed them feeding, in significant numbers, on deep-sea corals, notably “bamboo corals” in the family Isididae and related colonial octocorals (e.g. Mah 2020, 2022). It is common for video observations of Evoplosoma to be recorded rather than for specimens to have been collected.