Asteroschema tubiferum Matsumoto, 1911

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 tubiferum Matsumoto, 1911

Figures 12 , 13

Asteroschema tubiferum Matsumoto, 1911: 52; 1917: 44; Baker 1980: 22, fig. 4; McKnight 2000: 24, fig. 7.

Material examined.

China • 1 specimen; South China Sea , Zhongsha Islands, seamount; 13°36.20'N, 113°33.74'E; depth 1515 m; 30 Mar. 2020; Collecting event: stn. SC025; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; GenBank: OK044298 ; IDSSE-EEB-SW0077 • 1 specimen; South China Sea , East of Zhongsha Islands, seamount; 16°22.11'N, 116°06.60'E; depth 1619 m; 09 Aug. 2020; Collecting event: stn. SC028; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; GenBank: OK044297, OL712213 ; IDSSE-EEB-SW0106. Northwest Pacific • 1 specimen; near Mariana Trench, Southeast of Guam Island, deepsea seamount, 11°57.20'N, 141°28.67'E; depth 1377 m; 03 Sep. 2019; Collecting event: stn. SC034; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; GenBank: OK044296, OL712212 ; IDSSE-EEB-SW0078 .

Description.

IDSSE-EEB-SW0078: disc diameter 10 mm, length of arms 200 mm (Fig. 12 ).

Disc. Disc flat, slightly raised above arms, swollen in center (Fig. 12A, B ). Disc covered with smooth, small, closely spaced, and evenly rounded or polygonal granular ossicles, dense in disc center (seven or eight grains in 1 mm), but larger and polygonal at distal edge (six or seven grains in 1 mm) (Fig. 12C, D ). Radial shields not meeting in center, but converging (Fig. 12C ). Distal end of radial shields raised above disc and wider than proximal end (Fig. 12C ). Genital slits narrow, vertical on ventral interradii (Fig. 12E ). Jaws elongated, covered densely with granular ossicles (Fig. 12F ). Flattened, pointed, and spearhead-shaped teeth and granular ossicles that resemble lateral oral papillae at apex of jaw (Fig. 12F ). Ventral disc densely covered with granular and polygonal ossicles (seven or eight grains in 1 mm; Fig. 12F ). Adoral shields connected to first ventral arm segment and concealed by granular ossicles but outline of shields visible. Oral shields not discernible and adoral shield spine densely covered by ossicles (Fig. 12F ).

Arms. Arms at base wide, dorsally flattened, and swollen in first few free segments (Fig. 12G ). Arms distalwards from middle part narrowing and more cylindrical (Fig. 10H ). Swollen dorsal arm base and proximal end of arm covered with dense granular or polygonal ossicles similar to disc (five or seven grains in 1 mm), on middle segments with slightly separated granular ossicles (six or seven grains in 1 mm), and distally decreasing in size and separated (seven or eight grains in 1 mm) (Fig. 12G, H ). Granular ossicles on lateral arm plates slightly separated, but continuing along arm. Ventral arm near arm base covered with granular ossicles similar to ventral disc (seven or eight grains in 1 mm), but less dense on middle half (five or six grains in 1 mm), and distally widely separated or naked (six or seven grains in 1 mm) (Fig. 12I, J ). On first few arm segments, tentacle pore with extended tube (Fig. 12J ). First tentacle pore without arm spine (Fig. 12F ). First arm spine appears at second arm segment, and second arm spine at eighth segment. Inner arm spine cylindrical, one arm segment in length, with blunt thorny tip, and slightly club-shaped (Fig. 12K ). Outer arm spine smaller in size, with smooth to thorny tip (Fig. 12K ). Both arm spines equal in length at distal end of arm, and compound hook with three or four secondary teeth (Fig. 12L ).

Color. In live specimen, reddish brown on dorsal disc and arm, light brown on ventral disc and arm (Fig. 12 ).

Ossicle morphology.

Lateral arm plate with two arm spine articular structures, with large, separated muscle and nerve openings (Fig. 13A ). Inner arm spine distalwards from proximal part of arm cylindrical, with terminal projection, and thorny surface (Fig. 13B ). Outer arm spine cylindrical, with pointed tip with few thorns (Fig. 13C ). Distally arm spine turns into compound hook with four secondary teeth (Fig. 13D ). Arm and disc concealed by less dense, wider, and shorter granular ossicles (Fig. 13E ). Vertebrae with streptospondylous articulation, dorsally a large longitudinal furrow, ventrally with deep median longitudinal groove with lateral ambulacral canals, no oral bridge, podial basins relatively small (Fig. 13F-J ).

Distribution.

325-1800 m depth. New Zealand, Tasman Sea, Kermadec Islands, Bay of Plenty, Hawaii, Sagami Sea, the South China Sea, and Northwest Pacific seamount.

Remarks.

Asteroschema tubiferum was first described by Matsumoto (1911), then redescribed by Matsumoto (1917), Baker (1980), and McKnight (2000). These redescriptions are helpful to identify individual morphological character variation. Matsumoto (1911, 1917) mentioned that in Asteroschema tubiferum the first ten arm segments have an extended tube in the tentacle pore (a sheath around the tentacle) that is closely attached to the arm spine and this character is present in our specimens. Previously, A. tubiferum had been recorded from both North and South Pacific Oceans at a wide distribution range. However, this is the first record from the South China Sea. The specimens from our collection concur with previous redescriptions, but we noticed a few variations such as less densely packed ossicles on ventral and lateral arm. The A. tubiferum specimen from the South China Sea collection showed less dense granular ossicles on the ventral disc and arm. Asteroschema tubiferum strongly resembles A. rubrum , A. laeve , and A. inoratum , but the characters of the granulation pattern, tentacle scale on first few arm segments, shape of the arm and inner arm spine characters can be used to distinguish it from these species (Table 2 ).

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 12. Asteroschema tubiferum Matsumoto, 1911 (IDSSE-EEB-SW 0078) A dorsal view B ventral view C dorsal disc D skin on the arm E lateral disc F ventral disc G dorsal arm (proximal) H dorsal arm (middle) I ventral arm (proximal) J outer arm spine (proximal) K arm spines (middle) L arm spines (distal). Abbreviations: as adoral shield, ars arm spine, go granular ossicle, gs genital slit, iars inner arm spine, j jaw, oars outer arm 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 13. Asteroschema tubiferum Matsumoto, 1911 (IDSSE-EEB-SW 0078) A lateral arm plate B outer arm spine (middle) C inner arm spine (middle) D arm spine (distal) E skin from dorsal arm base (granular ossicles) F-J vertebrae F proximal view G distal view H lateral view I dorsal view J ventral view. Abbreviations: d dorsal, 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 (F, G, J): 500 µm (B, H, I); 300 µm (A, C-E).