Asterostegus maini McKnight, 2003

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

publication ID	https://dx.doi.org/10.3897/zookeys.1090.76292
publication LSID	lsid:zoobank.org:pub:3B13C71E-E11B-49D2-891C-050DBD514872
persistent identifier	https://treatment.plazi.org/id/DE5CCD8C-5876-5558-A5FC-7F735C61DA7E
treatment provided by	ZooKeys by Pensoft
scientific name	Asterostegus maini McKnight, 2003
status

Treatment

Figures 18 View Figure 18 , 19 View Figure 19

Asterostegus maini McKnight, 2003: 386-389, figs 1, 2.

Astroceras elegans McKnight, 1989: 25 (non Astroceras elegans Bell, 1917).

Material examined.

China • 2 specimens; South China Sea , near Xisha Islands archipelago, seamount; 16°47.79'N, 113°15.04'E; depth 602 m; 31 Mar. 2020; Collecting event: stn. SC009; ‘Shenhaiyongshi’ msv leg; preserved in -80 °C; GenBank: OK044303 View Materials ; IDSSE-EEB-SW0075; IDSSE-EEB-SW0076 GoogleMaps .

Description.

IDSSE-EEB-SW0076: disc diameter 32.2 mm, length of arms 240-250 mm, height of arm base 9.8 mm (Fig. 18A-M View Figure 18 ).

Disc. Disc circular and slightly inflated radially, with sunken interradial margins (Fig. 16A View Figure 16 ). Radial shields elongated, narrow, raised above the disc, extending nearly toward the disc center (Fig. 18B, C View Figure 18 ). Distal half of radial shield periphery covered by 10-12 (0.44 to 0.75 mm in width) large, club-shaped granules (Fig. 18C View Figure 18 ). Most of these granules cluster on distal end of radial shield (Fig. 18C View Figure 18 ). Entire disc, including radial shields, covered by thick skin (Fig. 18A-C View Figure 18 ). Adoral shields with slightly ovoid outline (Fig. 18E, F View Figure 18 ). Teeth spearhead-shaped, accompanied by granular domed lateral oral papillae but not visible in wet specimen (Fig. 18D-F View Figure 18 ). Proximally, adoral shields separated by triangular plate (Fig. 18F View Figure 18 ) Oral shields absent, and single or double row of two to six rounded, square, or irregular oral interradial plates beyond adoral shields (Fig. 18E, F View Figure 18 ). One median plate located between distal end of adoral shields, and slightly proximal to rest of oral interradial plates (Fig. 18E, F View Figure 18 ). Lateral interradial surface of disc slightly vertical and covered by thick naked skin, two conspicuous genital slits inside a large opening (Fig. 18G View Figure 18 ).

Arms. Arms simple, strong, and not branching (Fig. 18A View Figure 18 ). Cross section of arm base slightly rectangular (7.2 mm in width and 8.5 mm high), but distal half of arm more cylindrical and narrower (Fig. 18H-J View Figure 18 ). Proximal to middle region of dorsal arm slightly flattened, ventral surface slightly arched, and lateral surface vertical (Fig. 18J, K View Figure 18 ). Whole arm concealed by thick skin (Fig. 18H-K View Figure 18 ). Lateral arm plate on proximal half of arms bears three to five club-shaped granules (0.4-0.6 mm in width) (Fig. 18H View Figure 18 ), decreasing in size and number along arm and vanishing on distal half of arm (Fig. 18I View Figure 18 ). Ventral arm covered by naked skin (Fig. 18K View Figure 18 ). First one to two tentacle pores lack arm spines; second or third pore with two or three arm spines, similar in size (Fig. 18D View Figure 18 ). At proximal end of arms, arm spines short, thick, ovoid with more or less rounded tip with rough surface, at middle of arms club-shaped, transversely flattened (Fig. 18J, K View Figure 18 ). Arm spines turn into hook with two to three secondary teeth at distal end of arms (Fig. 18L, M View Figure 18 ).

Color. In live specimen, dorsal disc interradially dark brown but radial shields light brown. Ventral and lateral disc whitish brown, dorsal surface of proximal and middle regions of arms bright brown/red. Lateral and ventral surface of arms whitish brown, granules creamy white (Fig. 18 View Figure 18 ).

Ossicle morphology.

Lateral arm plate with two arm spine articular structures, middle half of arm with large and wide, separated muscle and nerve openings, depression on inner side (Fig. 19A, B View Figure 19 ). Arm spines large, short, flattened, and club-shaped with thorny surface (Fig. 19C, D View Figure 19 ). Vertebrae with streptospondylous articulation. Vertebrae on proximal to middle half of the arm large, flat with deep ventral groove, no oral bridge (Fig. 19E, F View Figure 19 ). Vertebrae on distal half of arm slightly longer, dorsally large median longitudinal furrow, and deep median longitudinal groove on ventral side, with oral bridge (Fig. 19G, H View Figure 19 ).

Distribution.

417-602 m in depth. New Zealand (Cook Island), South China Sea.

Remarks.

Asterostegus maini was first described by McKnight (2003), with type locality Cook Islands, South Pacific Ocean, and Okanishi and Fujita (2014) redescribed it. However, this is the first record of Asterostegus maini since the holotype. Here we recorded two specimens from the South China Sea (disc diameter 26 mm and 32.2 mm) and both are larger than the holotype (disc diameter 22 mm). Currently, three species belong to the genus Asterostegus : A. maini McKnight, 2003, A. tuberculatus Mortensen, 1933, and A. sabineae Okanishi & Fujita, 2014. Asterostegus tuberculatus differs from A. maini in granules being scattered across the whole disc including the radial shield, and only two to three stump-like granules on the dorsolateral arm plate ( McKnight 2003; Okanishi and Fujita 2014). Asterostegus sabineae differs from A. maini in large stump-like granules on the radial shield, only one oral interradial plate, and one or two large stump-like granules on the dorsolateral arm plate ( Okanishi and Fujita 2014). The number of oral interradial plates and their arrangement are highly variable within and between individuals (Fig. 18E, F, N View Figure 18 ). Previous studies on the holotype showed only one row with two to five interradial plates ( McKnight 2003; Okanishi and Fujita 2014). However, in our specimens, these are arranged in one or two rows with two to seven interradial plates in total (Fig. 18E, F, N View Figure 18 ). Therefore, one of the key morphological characters in the genus Asterostegus , the arrangement of oral interradial plates has to be modified. One specimen from the present study (IDSSE-EEB-SW0075, 26 mm disc diameter) showed some morphological variations, such as: small granules on the periphery of the disc and on few small areas on the ventral disc (Fig. 18O, P View Figure 18 ). These granules are extremely small compared to those on the radial shields and arms. In the specimens from the present study, first arm spines started from second or third arm segment, but in the holotype, it started from the fourth arm segment. However, except for these small morphological variations, both specimens were similar to the holotype description.

Kingdom	Animalia
Phylum	Echinodermata
Class	Ophiuroidea
Order	Euryalida
Family	Euryalidae
Genus	Asterostegus