Pergamaster triseriatus H.E.S. Clark 1962

Pergamaster triseriatus H.E.S. Clark, 1962

(Figures 15 A–D)

H.E.S. Clark, 1962: 46; 1963: 43

Distribution. Ross Sea. 256–1674 m.

Material examined. Ross Quadrant. USNM 1081980, center of Ross Sea, Southern Ocean. 76˚25’S, 170˚24’W to 76˚25’S, 170˚32’W, 568 m, Coll. Univ. Southern California (2 dry specimens, R=6.4, r=2.7, R=5.8, r=2.3); USNM 1082736, Center of Ross Sea, Southern Ocean. 76˚08’S, 165˚04’W to 76˚10’S, 165˚10’W, 494–498 m, Coll. Univ. Southern California (1 dry specimens, R=5.4, r=1.6); USNM 1081791, Victoria Land, Ross Sea. 74˚01’S, 178˚53’ to 73˚59’S, 179˚04’E, 256– 258 m. Coll. Univ. Southern California. (1 dry spec. R=4.07, r=1.67); USNM 1081792, Victoria Land, Ross Sea. 77˚35’S, 174˚58’ to 77˚35’S, 174˚59’E, 731 m. Coll. Univ. Southern California. (R=4.9, r=1.9); USNM 1081794 center of Ross Sea, Southern Ocean. 75˚50’S, 173˚08’W to 75˚52’S, 173˚08’W, 468–474 m, Coll. Univ. Southern California (1 dry spec, R=3.4, r=1.3); USNM 1081795 Victoria Land, Ross Sea, 72˚03’S, 172˚38’E, to 72˚04’, 172˚06’E, 344– 348 m., Coll. Univ. of Southern California (2 dry specs. R=4.2, r=2.2, R=3.8, r=1.6); USNM 1081796. Ross Sea. 76˚00’S, 176˚48’E to 76˚01’S, 176˚44’E, 566– 569 m. Coll. Univ. Southern California (1 dry spec. R=4.1, r=1.4); USNM 1081797 South of Cape Adare, Victoria Land, Ross Sea. 71˚16’S, 171˚45’E to 71˚16’S, 171˚35’E. 1565–1674 m. Coll. Univ. Southern California (2 dry specs. R=3.9, r=1.6; R=1.1, r=0.7); USNM 1082730 West of Ross Island, Victoria Land, Ross Sea. 77˚33’S, 174˚43’E to 77˚34’S, 174˚48’E, 728 m. Coll. Univ. Southern California (1 dry spec. R=2.2, r=1.2); USNM 1082744, West of Franklin Island, Ross Sea, 76˚30’S, 174˚54’ to 76˚33’S, 174˚58’E, 445–448 m, Coll. Univ. of Southern California (1 dry spec. R= 6.3, r=2.9); USNM 1082948, Victoria Land, Ross Sea. 75˚01’S, 168˚23’ to 75˚02’S, 168˚32’E, 334– 335 m. coll. Univ. Southern California. (1 dry spec. R=8.2, r=1.4); USNM 1086352 Ross Sea. 76˚00’S, 176˚48’E to 76˚01’S, 176˚44’E, 566–569 m, Coll. Univ. Southern California (3 dry specs. R=2.2, r=1.1, R=2.1, r=1.1, R=1.5, r=0.8, USNM 1087201 Victoria Land, Ross Sea. 76˚00’S, 172˚04’E to 76˚00, S, 172˚ 04’E. 565– 569.0 m. (1 coll. R=6.3, r=1.8); USNM 1090951 Center of Ross Sea 75˚50’S, 173˚08’ to 75˚51’S, 173˚08’E, 476 m. coll. Univ. Southern California (3 dry specs. R= 5.4, r=2.1, R=5.4, r=2.0, R=3.9, r=1.7); USNM 1091183 Victoria Land, Ross Sea. 73˚05’S, 173˚59’E to 73˚06’S, 174˚05’E, 339– 343 m. Coll. Univ. of Southern California (R=1.2, r=0.6); USNM 1121468. E. of Cape Adare, Ross Sea, 71˚23’S, 171˚12’E, 351–357 m (1 dry spec. R=6.0, r=2.7); USNM 1120478. E. of Cape Adare, Ross Sea, 71˚22’S, 170˚43’E, 160– 164 m. (1 dry spec. R=4.0, r=1.5); USNM 1121183, North of Cape Adare, Victoria Land, Ross Sea. 68˚05’S, 173˚44’E to 68˚05’S, 173˚38’E, 2608– 3175 m. Coll. Univ. Southern California (R=1.3, r=0.7).

Description. Disk surface thickened. stellate in shape, arms triangular, elongate (Fig. 15 B). Oral surface in dry preserved specimens are weakly concave. Interradial arcs weakly curved to linear (Fig. 15 A–C). R/r=1.9–3.4.

Abactinal plates weakly convex, smooth, with no accessories present on plate surface (Fig. 15 A, B, D). Each plate irregularly round to quadrate to polygonal in outline, variable in size (Fig. 15 B, C). Largest plates proximal on disk with smaller plates distally located adjacent to contact with superomarginal plate series. Up to three rows of abactinal plates extending along arm to within three to four superomarginal plates away from terminal plate. Carinal plates distinctly larger and more convex. Granules, two to 11, outline ranging from rectangular to triangular in shape, forming a discrete peripheral border around each abactinal that is not flush with other abactinal plaes. Granules relatively large, making up approximately 35–40% of the distance of each carinal plate. Abactinal plate surface within peripheral, granular border bare and smooth. Fasciolar grooves shallow to absent. Madreporite polygonal with well-developed sulci, flanked by five to six abactinal plates.

Marginal plates are round to quadrate in outline. Superomarginals, wider then long, with rounded edges and inferomarginals interradially becoming more elongate and rectangular interradially but becoming more more squarish closer to the armtip (Fig. 15 D). Superomarginals, 22–34, inferomarginals, 30–38 (both at R=~5.8) from armtip to armtip, forming rounded dorsolateral edge. Marginal plate surface flat to weakly convex and smooth, lacking any ornamentation or surface accessories with plate surfaces becoming more swollen and convex, especially near the terminal plate. Marginal granules, 18–36, flattened, angular to irregular in shape, forming distinct periphery. Peripheral granules on superomarginals more close-set and flush, becoming more spaced and less closely arranged around inferomarginals. Granules larger interradially, becoming smaller distally. Granules relatively large, comprising~30–35% of distance of marginal from one edge of periphery to the other across each plate. Terminal plate round, smooth, convex, strongly convex abutting two superomarginals (e.g., Fig. 14 F).

Actinal surface with actinal plates in approximately three to four chevrons, but so completely covered by angular granules that plate distinctions are unclear. Granules, polygonal to quadrate, but flat-topped to weakly convex, approximately four to seven per plate, forming a pavement over actinal surface. Granules larger proximally and more widely spaced, becoming smaller, more densely packed, and more irregular in shape adjacent to contact with inferomarginal plate series. Fasciolar channels produced by granular cover, shallow. Actinal plates extend along approximately 40–50% of arm distance.

Adambulacral plates wider than long with crowded armature. Furrow spines two (occasionally 3), blunt, very thick and oval-quadrate in cross-section (Fig. 15 C). Single subambulacral spine present, thick, round –ovaloid to triangular in cross-section with narrow base. Smaller subambulacrals present proximally becoming much larger progressively along adambulacral series. Distalmost subambulacrals are comparable in size and thickness to furrow spines. Adambulacral surface covered by approximately four to six, widely spaced pointed, angular or flattened granules. Discrete fasciolar space between adambulacral and actinal plate series.

Furrow spines on oral plate, two with a third projecting into mouth, one per plate (two project into mouth), thick, blunt, triangular in cross-section with rounded edges. Similar in thickness to furrow spines. Spines on oral plate surface are absent. Oral plate surface covered by granules, four, well-spaced, polygonal to angular in shape similar in appearance to those on adambulacral plate surface.

Pedicellariae not observed.

Juvenile/Small specimen. Smaller indiduals are weakly stellate (R/r=1.5 vs. R/r> 1.9 in larger specimens), disk large, arms, triangular.

Abactinal surface convex. Disk thickened. Plates polygonal to round in outline (similar to those in adults), with weakly convex, bare surface, but with size and shape more homogeneously distributed between disk edge and center. Peripheral granules, one to seven, round to angular in outline, discontinuous around abactinal plate. Other then peripheral granules, no other accessories present on plate surface. Madreporite weakly developed, flanked by three abactinal plates. Papular pores sometimes surrounded by three triangular granules in a triangular arrangement.

Marginal plates swollen, bare. Superomarginals slightly offset from inferomarginals, which are also narrower. Superomarginal plates, 14; inferomarginals 20 from armtip to armtip. Granules, ~9–18, forming discontinous periphery around superomarginal plates similar to those on abactinal plates. Granules on inferomarginals and on lateral side slightly larger, forming a more well-defined border around inferomarginal plates. Fasciolar groove present between superomarginal and inferomarginal plates becoming continuous with those on actinal surface. Some individual granules and continouously merged granules present on oral surface of inferomarginal plates

Actinal plates in two series, each plate irregular to quadrate in shape, with one to six large, irregular granules. Center of actinal plates, bare. Shallow fasciolar grooves continuous with those between marginal plates. Furrow spines two, thick, ovaloid in cross-section. Subambulacrals two, one elongate, thickened spine similar in appearance to furrow spine and another short spine approximately 1/3 of the length of the longer one. Granules, one to three on adambulacral plate surface. Middle region of adambulacral bare. Oral plates, similar to those in adults with four furrow spines. The proximalmost furrow spine projects into the mouth. Oral plate surface covered by thorny granules, three to five, angular in cross-section.

As with adults, no pedicellariae observed.