Asteroschema horridum Lyman, 1879

Nethupul, Hasitha, Stöhr, Sabine & Zhang, Haibin, 2022, New species, redescriptions and new records of deep-sea brittle stars (Echinodermata: Ophiuroidea) from the South China Sea, an integrated morphological and molecular approach, European Journal of Taxonomy 810 (1), pp. 1-95 : 18-21

Asteroschema horridum Lyman, 1879

Figs 7–8

Asteroschema horridum Lyman, 1879: 66 .

Asteroschema horridum – Lyman 1882: 275. — Baker 1980: 20, fig. 4. — McKnight 2000: 17, pl. 3.

Material examined

CHINA • 1 spec.; South China Sea , SE of Zhongsha Islands complex, seamount; 13°58.68′ N, 114°52.09′ E; depth 1550 m; 25 Sep. 2020; collection event: stn SC013; MSV Shenhaiyongshi leg.; preserved in 95% ethanol; GenBank: MZ 198759 ; IDSSE EEB-SW0005 • 1 spec.; South China Sea, SE of Hainan Island , seamount; 18°41.95′ N, 113°33.08′ E; depth 1070 m; 29 Mar. 2018; collection event: stn SC019; MSV Shenhaiyongshi leg.; preserved in -80°C; IDSSE EEB-SW0033 .

Description ( IDSSE EEB-SW 0005)

MEASUREMENTS. Disc diameter 12.5 mm, length of arms from 180 to 191 mm.

DiSC. Flat, interradially deeply excavated and small in relation to total body size of specimen. Disc covered with small, tumid, irregular scales, but larger on ventral than on dorsal disc. Conically tumid scales on radial shields, forming tubercles with finely thorny tip ( Fig. 7A–B ), both shields and tubercles decreasing in size towards disc center. Radial shields thick, swollen, widely separated distally, convergent proximally and with additional smaller scales and tubercles. Genital slits short, vertical on ventral interradii ( Fig. 7D ). Seven blunt, spearhead-shaped teeth. Jaws covered with swollen scales and no true oral papillae ( Fig. 7C–D ). Adoral shield obscured by swollen scales, oral shield absent and oral tentacle pore covered by small tube-shaped scales. Entire oral area covered with tumid scales, higher and pointier towards margin of ventral disc ( Fig. 7C ).

ARMS. Narrow, more cylindrical and slightly swollen in first 14–15 free arm segments ( Fig. 7E ). Dorsal and ventral arm also covered with more trapezoid tuberculous scales, distally tubercles more rounded and less elongated and arms with increasingly banded appearance distalwards ( Fig. 7E–I ). Tubercles on ventral arm slightly lower and pointier than on dorsal surface. First tentacle pore with zero to one arm spine, on second to fifth arm segments one arm spine at tentacle pores, thereafter two arm spines per pore ( Fig. 7G–H ). Arm spines cylindrical with thorny tip, innermost spine slightly swollen, longer than arm width, twice as long as outermost spine, with thorny tip. Outermost spine not swollen, half as long as innermost spine, tapered ( Figs 7I–J , 8C ).

COLOR. Pale reddish-brown in alcohol specimen ( Fig. 7 ), slightly stronger color in live specimen.

OSSiCLE MORPHOLOGY. Lateral arm plates curved around vertebrae, bearing two strongly outwards curved arm spine articulations with large muscle and nerve openings ( Fig. 8A–B ). Vertebrae with a streptospondylous articulation, with deep slope between proximal and distal end, ventrally with longitudinal groove along midline, no oral bridge ( Fig. 8D–H ).

Remarks

Asteroschema horridum was first described by Lyman (1879), with the Kermadec Islands as the type locality (HMS ‘Challenger’ Expedition). Baker (1980) and McKnight (2000) redescribed it. The specimen from our collection was similar to Lyman’s holotype description, but differs slightly from the descriptions in Baker (1980) and McKnight (2000) in having the start of the second arm spine at the first few arm segments (beyond segments 3–6, usually beyond segment 2). This character varies among species of Asteroschema ( Baker 1980) . Another morphological variation was shown as the extent of swelling on the proximal arm. In the present study, the small specimen (8.2 mm) had a swollen arm for five to six segments, which is similar to Baker (1980) and McKnight (2000), but they did not mention the diameter of the disc (size of the specimen). The character of having a small, flat disc with tubercleshaped scales is one that distinguishes A. horridum from other species of Asteroschema . Asteroschema horridum is considered a close relative of A. tumidum Lyman, 1879 according to morphological aspects ( Baker 1980; McKnight 2000). Previously published descriptions suggested that the morphological characters of A. horridum may vary with the size and maturity of the specimens ( Baker 1980; McKnight 2000).

Distribution

300–2000 m depth. South China Sea, Kermadec Islands and Norfolk Island ( New Zealand), New Caledonia, Vanuatu (Coral Sea), French Polynesia ( Baker 1980; McKnight 2000; OBIS 2021).

Figures

Fig. 7. Asteroschema horridum Lyman, 1879 (IDSSE EEB-SW0005). A. Dorsal disc. B. Ventral disc. C. Oral frame. D. Lateral disc. E–F. Dorsal arm (proximal and distal regions).G. Ventral arm.H. Lateral arm. I. Ventral arm. J. Ventral arm spine. Abbreviations: ars = arm spine; das = dorsal arm spine; gs = genital slit. Scale bars: A–B, D–I = 2 mm; C = 1 mm; J = 500 µm.

Fig. 8. Asteroschema horridum Lyman, 1879, SEM (IDSSE EEB-SW0005). A–B. Lateral arm plate (external, internal). C. Arm spine. D–H. Vertebrae. D. Proximal view. E. Distal view. F. Ventral view. G. Dorsal view. H. Lateral view. Abbreviations: D = dorsal; Dist = distal; Prox = proximal; mo = muscle opening; no = nerve opening; V = ventral. Scale bars: A–C, F = 300 µm; D–E, G–H = 500 µm.