Evoplosoma Fisher 1906

Mah, Christopher L., 2023, New Goniasteridae and in situ observations significant to deep-sea coral predation, Memoirs of Museum Victoria 83, pp. 1-35 : 15-16

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, 2015b: 2; 2022: 42

Diagnosis (from Mah, 2015b). Body strongly stellate. Arm narrow, elongated. R/r 2.3–4.11 (most 3.0–4.0). Interradial arcs straight to weakly curved. Abactinal plates, flat and platformlike. 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 surfaces. Marginal plates generally quadrate in shape, some showing direct 1:1 superomarginal/inferomarginal correspondence, but others being more offset. Marginals relatively numerous, 30–70 per interradius. Some species with bare marginal plate surface, but most with even to dense granule covering. Granules vary from having rounded surfaces 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 on all species. Primary spines on actinal plate surface in most species. Furrow spines varying in number from 2 to 12. 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 11 species known from lower bathyal to abyssal settings (1000–3000 m) primarily in the Atlantic and the Pacific, with a single species, Evoplosoma augusti Koehler 1909 , known from the Indian Ocean. Mah (2015b) provided an overview and key to known Evoplosoma species. Most species have been recorded from relatively few specimens, in many cases only from the holotype (e.g. Mah et al., 2010, Mah, 2015). As remotely operated video investigation has become increasingly common and deep-sea coral habitats are explored, Evoplosoma and/or related hippasterines, such as Hippasteria , are now observed with increasing frequency (e.g. Mah, 2015, 2022) and in situ density and abundance recorded.

Evoplosoma shows morphological affinities, such as prominent spines on abactinal and marginal plates as well as granule-covered abactinal plates, with other newly described goniasterid genera, such as Atheraster . Atheraster in turn, shares characters such as the presence of enlarged abactinal arm plates relative to disk plates, with Circeaster .

Prior to the four species reported herein, only E. tasmanica (McKnight, 2006) , from Tasmanian waters, was known from the South Pacific adjacent to Australia and New Zealand.

Key to Evoplosoma in Australian and adjacent waters

(0) Fleshy dermis invested with granules, abactinal spines present or absent. Granules absent from marginal plate surface. (1)

(1) No spines on abactinal surface. Furrow spines 4–6. Evoplosoma voratus Mah

(1’) Abactinal surface invested with conical spines. Furrow spines nine to ten. Evoplosoma pharos n. sp.

(0’) Dermis not fleshy or soft, surface covered by coarse, granules and distinct, or conical abactinal spines. Granules present on marginal plate surface. (2)

(2) Furrow spines 5–8. Spines, large, widely spaced, thick, conical with pointed or blunt tips present on abactinal and marginal surface. Evoplosoma timorensis Aziz and Jangoux 1985a

(2’) Furrow spines four or fewer. Abactinal spination present, but spines short, bullet-like, weakly expressed or absent. (3)

(3) Abactinal surface with no primary spines, covered by plates with pointed to coarse-sized granules, widely spaced. Evoplosoma tasmanica McKnight 2006

(3’) Short, conical spines covering abactinal surface. Coarse granules forming continuous covering on abactinal, marginal and actinal surface. (4)

(4) Superomarginal plates each with a single prominent, conical spine in series along the arm, although two or three are present on interradial plates. Granules angular with convex to pointed tips, cover abactinal, marginal, actinal surface. Evoplosoma mystrion n. sp.

(4’) Interradial plates with three prominent spines decreasing to two then a single spine with none on distalmost marginal plates. Granules coarse, blunt tipped and blocky, forming continuous cover over abactinal, marginal, actinal surface. Evoplosoma besseyae n. sp.