Asteroschema rubrum Lyman, 1879

Nethupul, Hasitha, Stoehr, Sabine & Zhang, Haibin, 2022, Order Euryalida (Echinodermata, Ophiuroidea), new species and new records from the South China Sea and the Northwest Pacific seamounts, ZooKeys 1090, pp. 161-216 : 161

Asteroschema rubrum Lyman, 1879

Figures 10 , 11

Asteroschema rubrum Lyman, 1879: 68-69, fig. 17, figs 454-457.

Material examined.

China • 3 specimens; South China Sea , near Zhongsha Islands, seamount; 13°55.44'N, 115°25.37'E; depth 958 m; 09 Mar. 2020; Collecting event: stn. SC007; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; GenBank: OK044293, OL712209, OK044294, OL712210, OK044295, OL712211 ; IDSSE-EEB-SW0071, IDSSE-EEB-SW0072, IDSSE-EEB-SW0073 • 1 specimen; South China Sea , near Zhongsha Islands, seamount; 14°21.93'N, 115°23.89'E; depth 922 m; 17 Mar. 2020; Collecting event: stn. SC035; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; IDSSE-EEB-SW0088 .

Description.

IDSSE-EEB-SW0072: disc diameter 12 mm, length of arms from 165-175 mm (Fig. 10 ).

Disc. Disc flat, slightly raised above arms, swollen in center, and small in relation to total body size of specimen (Fig. 10A, B ). Disc covered with smooth, dense, evenly distributed, small rounded or irregular granular ossicles, similar in size (seven or eight granular ossicles in 1 mm; Fig. 10C, D ). Radial shields closely together, parallel, raised above distal disc edge, but mostly concealed by skin with granular ossicles (Fig. 10C ). Radial shields do not meet in center. Genital slits wide and vertical on ventral interradii (Fig. 10E ). Jaw large, long and covered with dense irregular ossicles (Fig. 10F ). Spearhead-shaped teeth and granular ossicles that resemble lateral oral papillae at apex of jaw (Fig. 10F ). Adoral shields large, connected to first ventral arm segment, and concealed by granular ossicles (Fig. 10F ). Oral shields not discernible and adoral shield spine naked. Whole oral region swollen nearly to genital slit. Ventral disc covered with dense granular ossicles (seven or eight grains in 1 mm; Fig. 10F ).

Arms. Arms at base wide, not arched, dorsally flattened, and slightly swollen in first few free segments (Fig. 10A, G ). Arms distalwards from middle part narrowing and more cylindrical (Fig. 10H ). Dorsal arm base covered with smooth rounded granular ossicles (six or seven grains in 1 mm), middle segments with dense granular ossicles all the way to the arm spine base (seven or eight grains in 1 mm), and distally decreasing in size and separated (seven or eight grains in 1 mm) (Fig. 10G-L ). Ventral arm base covered with dense granular ossicles similar to the ventral disc (eight or nine grains in 1 mm), distally decreasing in size and separated to naked (Fig. 10H-K ). First one to two tentacle pores without arm spine (Fig. 10F ). First arm spine appears at second or third arm segment, and second arm spine at ninth or eleventh segment (Fig. 10I ). Outer arm spine half as long as inner spine in middle region, thorny pointed tip, distally compound hook (Fig. 10K, L ). Inner arm spine cylindrical, one to one and a half arm segment in length, initially tapering to a pointed thorny tip, in middle blunt, slightly swollen with thorny surface on more than half its length, distally compound hook with three or four secondary teeth (Fig. 10I-L ).

Color. In live specimen, reddish brown (Fig. 10 ).

Ossicle morphology.

Lateral arm plate with two arm spine articular structures, with slightly separate large muscle and nerve openings (Fig. 11A ). A depression on inner side of lateral arm plate (Fig. 11B ). Inner arm spine from proximal and middle half of arm cylindrical, slightly swollen, with thorny tip (Fig. 11C ). Distally arm spine turns into compound hook with secondary teeth (Fig. 11D ). Arm and disc concealed by granular ossicles, slightly wider than high, round to short stumps with convex tip (Fig. 11E ). Vertebrae with streptospondylous articulation, with deep slope between proximal and distal end, dorsally a median longitudinal groove, ventrally with median deep longitudinal groove with lateral ambulacral canals, podial basins moderate in size (Fig. 11F-J ).

Distribution.

730-958 m depth. Near Brandella, Chile and in the South China Sea.

Remarks.

Asteroschema rubrum was first described by Lyman (1879), with type locality in the Southwest Pacific Ocean near South America. This is the first rediscovery after the original description. The specimens from our collection concur well with Lyman’s holotype description, the only difference was the starting point of the second arm spines. However, this morphological character is highly variable among individuals. According to the holotype description, A. rubrum belongs in the clade with granular ossicles only in the genus Asteroschema , but Okanishi and Fujita (2009) considered A. rubrum in the clade with conical and granular ossicles. Although, the SEM images of granular ossicles in the skin appear as granular to somewhat small stumps with convex tip (Fig. 11E ). However, the description of the holotype is identical with our specimen, and it was described as granular ossicles. The characters of the swollen oral region, smooth granulation on the disc, and innermost spine can be used to distinguish A. rubrum from other species of Asteroschema (Table 2 ). The dorsal disc of A. rubrum seems naked in wet condition due to its smooth granulation which can lead to misidentification as Ophiocreas species (Fig. 10A ). This is the first record from the South China Sea.

Figures

Figure 10. Asteroschema rubrum Lyman, 1879 (IDSSE-EEB-SW 0072) A dorsal view B ventral view C dorsal disc D skin on the disc E lateral disc F ventral disc G dorsal arm (proximal) H lateral arm (middle) I ventral arm (proximal) J outer arm spine (proximal) K arm spines (middle) L arm spines (distal). Abbreviations: as adoral shield, ass adoral shield spine, ars arm spine, go granular ossicle, gs genital slit, iars inner arm spine, j jaw, oars outer arm spine, ass adoral shield spine, rs radial shield, t teeth, tp tentacle pore. Scale bars: 2 mm (A, B); 1 mm (E-G, I); 500 µm (C, H, J, K); 200 µm (D, L).

Figure 11. Asteroschema rubrum Lyman, 1879 (IDSSE-EEB-SW 0072) A, B lateral arm plate (external, internal), C outer arm spine (middle), D arm spine (distal), E skin from dorsal arm base (rounded to somewhat cone shaped granular ossicles), F-J vertebrae; F proximal view, G distal view, H lateral view, I dorsal view, J ventral view. Abbreviations: d dorsal, de depression, dist distal, lac lateral ambulacral canals, mo muscle opening, no nerve opening, pb podial basin, prox proximal, st secondary teeth, v ventral. Scale bars: 800 µm (C); 500 µm (A, F, G); 300 µm (B, E, H-J); 200 µm (D).