Evolosoma forcipifera 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 : 43-46

Evolosoma forcipifera Fisher 1906

FIGURE 14 A–F

Fisher 1906: 1065; Mah 2015: 5.

Diagnosis. Body strongly stellate (R/r=2.3=2.72), interradial arcs weakly curved with acutely triangular arms showing pointed arm tips. Abactinal, marginal, actinal surface covered with large sharp, pointed conical spines. Abactinal, marginal and actinal surface covered by thick dermis embedded with coarse granules with blunt to pointed tips. Marginal plates primarily with lateral facing, each with large single, conical spine and 1 to 2 paddle-shaped pedicellariae. Paddle-shaped pedicellariae present on actinal surface. Furrow spines, two to four, one enlarged subambulacral spine round in cross-section with pointed to broad blunt, truncate tips. An elongate bivalve pedicellariae (length=~3.0 mm) with broad wide valves present adjacent to subambulacral spines. Adambulacral plates with 6 to 10 large coarse granules,

Comments. Evoplosoma forcipifera was the first species of Evoplosoma to be described but the holotype is apparently lost (Ahearn 1995). Relatively few specimen records are known, including one from off Oahu ( Mah 2015a) from 2305 m and the specimen record herein from the Wake Island region.

The Wake Island specimen shares many characters listed in Fisher’s (1906) description, including surface covered by conical spines, spatulate or paddle-like pedicellariae, two to four furrow spines (mostly three or four in Fisher), in addition to an enlarged subambulacral spine and adambulacral pedicellariae along the tube foot furrow. It demonstrated a deep-red/orange color. Although video observations did not permit perfect identifications, several fine details, such as furrow and subambulacral spine number, could be counted and identified from close-ups taken by the ROV.

In situ observation of this species shows the radial regions on the disk to be strongly convex with papulae widely extended, suggesting that it has swollen its coelomic cavity with water.

Feeding Observations. This species was observed feeding primarily on octocorals in the family Isididae , the “bamboo corals,” with two unusual observations including predation on Iridigorgia, a chrysogorgiid or “golden coral”, (EX1603_IMG_20160229T004700Z_ROVHD_COR_ASR_FSH_AUD.jpg) and the specimen herein which was observed feeding on an octocoral in the Primnoidae ( Fig. 14B ) (EX1606_IMG_20160812T010019Z_ROVHD_ ASR_COR.jpg). Feeding apparently proceeds from the base of the coral with the star using its tube feet to climb up the colony, using its extended cardiac stomach to digest the polyps and other tissue down to the stalk. In every observation, the stalk is placed directly along the tube foot groove with its stomach and disk hunched over the tissue as the animal ascends. Some observations (e.g. EX1708_IMG_20170914T234616Z_ROVHD.jpg) showed more than one barren stalk adjacent to the central one the animal was climbing suggesting that this species exploits more than one branch at a time during feeding. One image (EX1606_IMG_20160809T023948Z_ROVHD_ASR_AUD_HL.jpg) showed a pyloric stomach, which was almost the entire distance of the disk, extended upon an unidentified cnidarian stalk. Another image from the Musicians Seamount chain (EX1708_IMG_20170916T235310Z_ROVHD.jpg) showed two individuals ascending an isidid octocoral colony, which displays multiple bare basal stalks with several full tips remaining intact, suggesting that the E. forcipifera might not fully attack polyps along the entirety of the colony’s height.

Occurrence: Hawaiian Islands, Wake Island, 929–2305 m.

Description. Body strongly stellate (R/r=2.72), disk and body swollen. Interradial arcs weakly curved with acutely triangular arms showing pointed arm tips ( Fig. 14A ).

Abactinal surface covered by a thick dermal cover, embedded with coarse granules ( Fig. 14 A-inset). Individual granules approximately 2 granules counted along a 1.0 mm line, each granule quadrate to polygonal in outline. Abactinal granules forming continuous cover with those on marginal plates. Granules are evenly distributed along surface. Surface covered by short, conical spines (about 1.0– 1.5 mm in height) present along midradius of each arm, but also scattered interradially, especially on disk. Spines mostly absent from abactinal surface on arms. Papulae present all over the abactinal surface, especially along radial regions on disk and arms, absent interradially. Paddleshaped pedicellariae present all over the disk surface with many sitting adjacent to conical spines ( Fig. 14 A-inset). Madreporite weakly convex, inset onto abactinal surface surrounded by five to six conical spines, 19–22 granules form periphery around each madreporite. Distinct depression present in each interradius ( Fig. 14A ).

Superomarginals 38, inferomarginals 36–38, most of each spine series with large, single, conical spine on most plates. Superomarginal plates more lateral-facing on disk, becoming more abactinal facing along arm, especially near armtip ( Fig. 14D ). Disk plates present up to armtip. Superomarginals quadrate in shape, especially equal sized (L=W) interradially becoming wider distally along arm. Inferomarginals are mostly equal sized (L=W). Superomarginal spines form distinct series on abactinal-lateral edge on superomarginal and inferomarginal/actinal edge on inferomarginals ( Fig. 14D ). Interradial inferomarginals with two to four short conical spines with pointed tips becoming larger, single prominent spines on arms extending to armtips. Both superomarginals and inferomarginals, especially interradial plates with one or two paddle-shaped pedicellariae (about 1.0 mm across) sitting near to or adjacent to large conical spine. Spine bases devoid of granules, especially distinct along arm. Both marginal plate series with covering of coarse granules identical to those on the abactinal plate surface ( Fig. 14F ). Some granules on interradial plates with pointed tips but most are flattened, distributed evenly along plate surface with poor distinction between peripheral and central granules ( Fig. 14F ). Terminal plate large (approximately 3 times the size of adjacent superomarginal plates), round, convex with smooth surface.

Actinal surface in approximately three to four complete and one or two incomplete series but surface is completely covered by coarse granules, numbering two along a 1.0 mm line, identical in appearance to those on abactinal, marginal surfaces. Individual granules quadrate to polygonal in outline, evenly distributed along surface obscuring any plate contacts on actinal surface. Inferomarginal plates also with partial facing actinally. Actinal plate surface with sharp, conical spines ( Fig. 14E, F ), identical to those on superomarginal, abactinal surfaces, most heavily distributed distally adjacent to inferomarginal plates becoming weakly distributed to absent proximally to centrally on actinal plate surface. Large (1.0–2.0 mm tall) paddle-shaped pedicellariae similar to those on other surfaces on actinal surface ( Fig. 14C inset) especially adjacent to spines on distal surface adjacent to inferomarginal plates. Pedicellariae present one per plate on actinal plate series adjacent to adambulacral plate series.

Furrow spines, two to four with three or four ( Fig. 14E ) on proximal plates, variably with a minority displaying two or four. Distalmost furrow spine number decreasing to two. Central furrow spines tallest with those away from central spines shortest but all comparable in thickness. Furrow spines quadrate in cross-section, widely spaced, no adambulacral accessories present on surface immediately between furrow spines and subambulacral accessories. Furrow spines pointed, for some, triangular in cross-section. Adambulacral plates with one enlarged subambulacral spine ( Fig. 14E ), round in cross-section with pointed to broad blunt, truncate tips. Subambulacral spine about 10% thicker and longer than thickest furrow spine. An elongate bivalve pedicellariae (length=~3.0 mm) with broad wide valves present adjacent to subambulacral spines. Adambulacral plates with 6–10 large coarse granules, polygonal in outline, evenly spaced. Oral plate furrow spines eight per plate, with one larger furrow spine proximally at the oral end of the furrow spines. One large spine on tip of each oral plate (paired spines directed into the mouth). Oral plate surface each with a large bivalve pedicellariae present on each plate (two per interradius). Oral plate surface covered by 10–12 thick, blunt granules widely spaced, triangular to quadrate in outline.

Color in life is orange ( Fig. 14B ).

Material Examined: USNM 142429, East Wake Atoll, guyot 50 m south of Wake, Wake Island region, 18.4705, 166.681, 1409 m, Coll. NOAA Ship Okeanos Explorer (ROV- Deep Discoverer ), 12 August 2016 EX 1606. 1 wet spec. R =6.8 r=2.5. EX 1606_20160812 T 011833_D2_ DIVE 10_ SPEC 02BIO_C01 EX 1606_IMG_ 20160812 T 010019Z_ ROVHD _ ASR _COR.jpg

Images Examined feeding on Isididae . Salmon Bank , Hawaiian Islands, 26.81791063, -176.3146419, 1970 m. EX1504 L2_IMG_20150811 T215149 Z_ ROVHD _ ASR _EATING_COR.jpg .

Lone Cone Seamount , Hawaiian Islands, 15.59132996, -167.7464867, 1936 m

feeding on Isididae . EX 1504L4_IMG_20150921 T 223956Z_ ROVHD _COR_ ASR.jpg

feeding on Primnoidae . West Wake Atoll, Wake Island region, 18.47047761, 166.6806318, 1409 m. EX1606 _IMG_ 20160812 T010019 Z_ ROVHD _ ASR _COR.jpg

feeding on Isididae . Hawaiian Islands region , 26.64675054, -175.3950478, 1600 m EX1603 _IMG_20160306 T012800 Z_ ROVHD _ ASR _EAT_COR_ TIGHT.jpg

feeding on Iridigorgia. French Frigate Shoals, Hawaiian Islands , 23.94554586, -166.0417985, 1088 m EX1603 _IMG_20160229 T004700 Z_ ROVHD _COR_ ASR _ FSH _ AUD.jpg

Kingman Cone , Central Pacific region, 6.36542226, -162.3059529, 1027 m

feeding on Isididae . EX 1705_IMG_20170512 T 213429Z_ ROVHD.jpg

Mozart Seamount , Musicians Seamount region, 28.96183066, -162.0711676, 2316.8 m. EX1708 _IMG_20170921 T004516 Z_ ROVHD.jpg

feeding on Isididae . Tropic of Cancer Seamount , Musicians Seamount region, 23.30643303, -158.3573676, 1851 m. EX1708 _IMG_20170907 T201657 Z_ ROVHD.jpg

feeding on Isididae . Shostakovich Seamount , Musicians Seamount region, 33.25079287, -164.7668389 2706 m. EX1708 _IMG_20170916 T235310 Z_ ROVHD.jpg

feeding on Isididae . Shostakovich Seamount , Musicians Seamount region, 33.2507908, -164.7668429, 2706 m. EX1708 _IMG_20170916 T235151 Z_ ROVHD.jpg

feeding on Isididae . Mendelssohn Seamount , Musicians Seamount region, 25.16056974, -161.64448, 1777 m. EX1708 _IMG_20170925 T201613 Z_ ROVHD.jpg

fed on Isididae . North of the Hawaiian Islands Musicians seamount region. 26.5967583, -160.6715702, 1929 m. EX1708 _IMG_20170923 T232800 Z_ ROVHD.jpg

feeding on Isididae . Mendelssohn Seamount , Musicians Seamount region, 23.30738508, -158.3572373, 1793 m. EX1708 _IMG_20170925 T220607 Z_ ROVHD.jpg

feeding on Isididae . Tropic of Cancer Seamount , Musicians Seamount region, 20.44393307, 163.7155228, 1934.6 m. EX1708 _IMG_20170907 T215807 Z_ ROVHD.jpg

feeding on Isididae . Musicians Seamount region , 31.85123703, -162.8980554, 2254 m. EX1708 _IMG_20170914 T234616 Z_ ROVHD.jpg

Figures

FIGURE 14. Evoplosoma forcipulifera Fisher, 1906. USNM 142429 A. Abactinal view. Scale bar=5.0 mm. Inset showing close-up of abactinal plate including madreporite. Madreporite diameter=2.0 mm. B. In situ observation of specimen feeding. C. Actinal view. Scale bar=5.0 mm. Inset showing pedicellariae and actinal surface texture. Pedicellariae length=1.0 mm. D. Abactinal-lateral view showing superomarginal and inferomarginal plates and accessories. Scale bar=5.0 mm. E. Adambulacral armature-furrow spines, subambulacrals and etc. Scale bar=2.0 mm. F. Actinal and lateral surface showing marginal plate surface and spination. Scale bar=5.0 mm.