Astrodendrum cf. sagaminum ( Doederlein , 1902)

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

Astrodendrum cf. sagaminum ( Doederlein, 1902)

Figures 20 , 21

Astrodendrum sagaminum Döderlein, 1902: 321-322; 1911: 38-39, figs 2, 3-5, 7, 8; 1927: 32, 92; H.L. Clark 1911: 292-293; A. H. Clark 1916a: 185; Liao 2004: 109-111, fig. 52.

Material examined.

China • 1 specimen; South China Sea , East side from 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: OK044304 ; IDSSE-EEB-SW0104 .

Description.

Disc diameter 62 mm (Fig. 20A, B ).

Disc. Dorsal disc slightly inflated, swollen in the center (Fig. 20A, B ). Radial shields elongated, tapered at proximal end, extending to center of disc (Fig. 20C, D ). Entire disc covered by skin with conical ossicles of various size (0.4-0.7 mm high) and widely separated and scattered (Fig. 20C-E ). Genital slits conspicuous, interradial margin covered by two rows of higher than wide conical ossicles (Fig. 20F, G ). Ventral disc almost naked, but micro-granular ossicles visible on oral region (Fig. 18H ). Oral area covered by smooth skin with few scattered small granular ossicles, exposing adoral and oral shield outlines (Fig. 20H ). Oral plates flat, polygonal, and slightly in contact with adoral shields (Fig. 20H ). Adoral shields short, square. Oral papillae and teeth spiniform (Fig. 20H ), several vertical rows of teeth on dental plate (possibly tooth papillae at ventral edge).

Arms. Arms branched at least eight to nine times, flexible dorso-ventrally, flat ventrally, arched dorsally (Fig. 20I-N ). Ventral arm surface covered by smooth skin; proximal half with widely scattered small, flat, polygonal granular ossicles (Fig. 20I-K ). Dorsal arm surface covered by polygonal or domed plates and between these pedicellarial bands (Fig. 20L-O ) that appear after second arm fork, covering whole lateral to dorsal area of arm, creating annulated appearance (Fig. 20L ). First arm segment lacks spines, next four to six with two arm spines, thereafter two or three arm spines per segment (Fig. 20I-K ). Ventral arm spines similar in size, smaller, unevenly pointed, distally turning into hooks with 2-3 secondary teeth (Fig. 20K, P, Q ).

Color. In live specimen, whole specimen brown, but radial shields, oral regions, and ventral arms lighter than disc (Fig. 20 ).

Ossicle morphology.

On middle half of arm, lateral arm plates with perforations on ventral side, large muscle opening and small nerve opening (Fig. 21A ). Pedicellarial bands formed by approximately 12 articulating tubercles at curved distal end of baseplate and these articulations have a single foramen per tubercle for pedicellariae with one secondary tooth (Fig. 21B, C ). Ventral arm spines on distal end of arm transformed into hook with two or three secondary teeth (Fig. 21D ). Pedicellariae differ from ventral arm spine by having smooth apophysis (Fig. 21C, D ). Vertebrae with streptospondylous articulation with smooth lateral furrows and paired openings in lateral side of vertebrae for lateral ambulacral canals, no oral bridge (Fig. 21F-N ).

Distribution.

90-1300 m depth. South China Sea, Japan, East China Sea, Sri Lanka.

Remarks.

The specimen is similar to the holotype description by Döderlein (1902), and the redescriptions of Döderlein (1911, 1927), Liao (2004) and Okanishi and Fujita (2018), but showed some morphological variations especially on the disc (Fig. 20 ). Therefore, we hesitate to fully associate our specimen with Astrodendrum sagaminum . All descriptions mentioned granules on both dorsal and ventral disc, but in the present specimen, the dorsal disc is covered with widely separated conical stump-like granules and the ventral disc is covered with widely scattered micro-polygonal ossicle plates in naked skin. However, Baker (1980) mentioned that the granular pattern on the disc was not a suitable morphological feature to delimit species in the genus Gorgonocephalus . This is the first record of Astrodendrum sagaminum from the South China Sea, if this is indeed that species.

Figures

Figure 18. Asterostegus maini McKnight, 2003 (A-M IDSSE-EEB-SW 0076 N-P IDSSE-EEB-SW 0075) A dorsal view B center of dorsal disc C dorsal disc (distal end of radial shields) D ventral disc E, F oral frame G lateral disc H dorsal arm (proximal) I dorsal arm (distal) J lateral arm (proximal) K ventral arm (middle) L, M arm spines (distal) N oral frame O periphery of the disc P oral frame (small transparent ossicles). Abbreviations: as adoral shield, ars arm spine, go granular ossicle, gs genital slit, j jaw, mp median plate, oip oral interradial plate, rs radial shield, t teeth, tp tentacle pore, ts tentacle scale. Scale bars: 6 mm (A); 2 mm (B-H, N); 1 mm (I-K, O, P); 500 µm (L); 200 µm (M).

Figure 20. Astrodendrum cf. sagaminum (Doederlein, 1902) (IDSSE-EEB-SW 0104) A dorsal view B ventral view C dorsal disc (center) D dorsal disc (distal edge) E radial shield F, G ventral disc H oral frame I, J ventral view of arm base K ventral view of after second arm branch L, M dorsal view of second arm branch N lateral view of arm (middle) O lateral view of arm (pedicellariae with baseplate) P, Q variations of arm spine on distal end of the arm. Abbreviations: ars arm spine, co conical ossicles gs genital slit, os oral shield, peb = pedicellarial band, rs radial shield, t teeth, tp tentacle pore. Scale bars: 16 mm (A, B); 2 mm (C, D, F, L); 1 mm (E, H-K, M, N); 500 µm (G, O); 200 µm (P, Q).

Figure 21. Astrodendrum cf. sagaminum (Doederlein, 1902) (IDSSE-EEB-SW 0104) A lateral arm plate (middle) B plan view of baseplate C pedicellariae D arm spine on distal end E-J vertebrae on middle half of arm E proximal view of branch vertebrae F proximal view G distal view H lateral view I dorsal view J ventral view K-N vertebrae on distal end of arm K distal view L proximal view M lateral view N ventral view. Abbreviations: ap articular pad of the base, au auricle, d dorsal, dist distal, fo foramina of the base, fs fossa between adjacent tubercles, hd head of the apophysis, lac lateral ambulacral canals, mo muscle opening, no nerve opening, pd pedicel of the apophysis, prox proximal, pt primary tooth of the blade, sh sheath of the baseplate, su sulcus of tubercle head, v ventral. Scale bars: 800 µm (E-J); 500 µm (A, B); 300 µm (K-N); 200 µm (D); 80 µm (C).