Asterostegus maini McKnight, 2003

Okanishi, Masanori & Fujita, Toshihiko, 2014, A taxonomic review of the genus Asterostegus (Echinodermata: Ophiuroidea), with the description of a new species, European Journal of Taxonomy 76, pp. 1-18 : 9-12

Asterostegus maini McKnight, 2003

Fig. 6

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

Asterostegus maini McKnight, 2003: 386-389, figs 1, 2 (replacement name).

Asterostegus maini – Okanshi & Fujita 2013: 568, 571, 575, fig. 1, tables 2-3.

Diagnosis

About 10 tubercles present on periphery of radial shields, ca. 250–300 µm long. On proximal portion of arm, three to five tubercles on top of each lateral bar. Three to five oral interradial plates forming one row.

Type material

Holotype ( NIWA 7564 , H-733), ethanol preserved specimen, vicinity of Pukapuka Atoll , Manihiki Plateau, Cook Islands, New Zealand, 10˚53.0’S, 165˚55.2’W – 10˚52.4’S, 165˚55.4’W, 417-446 m depth, 21 Apr. 1986.

Description

MEASUREMENTS. NIWA 7564, H-733: disc diameter 22 mm, arm length at least 205 mm (arms convoluted).

DISC. Disc circular in shape with notched interradial margins ( Fig. 6A-B ). On aboral surface, radial shields and their surrounds tumid ( Fig. 6A, C ). Aboral surface of the disc covered by skin and clubshaped tubercles on periphery of radial shields, ca. 250-300 µm ( Fig. 6C ). Radial shields, ca. 10.0 mm long and 1.7-2.1 mm wide, and completely covered by skin ( Fig. 6D ). Oral surface of the disc covered by skin ( Fig. 6E ). Seven to eight spear head-shaped teeth forming a vertical row on dental plate ( Fig. 6E ). Domed and granule-shaped oral papillae lying on each side of jaw, but can not be seen when wet ( Fig. 6E ). Two or three oral interradial plates form a row on proximal side of adoral shields but cannot be seen clearly when wet ( Fig. 6F ). The oral interradial plates projecting from lateral side of the disc ( Fig. 6G ). Lateral interradial surface of the disc nearly vertical, covered entirely by skin ( Fig. 6G ). Two genital slits in each interradius, 1.6 mm long and 0.2 mm wide ( Fig. 6G ).

ARMS. Arms simple, five in number, with no abrupt gap in width due to presence of gonads in proximal portion of arms. Arms tapering gradually distally. Proximal portion of the arms 6.7 mm wide and 7.1 mm high, oblong in cross-section. Aboral surface arched and oral surface flattened from middle to distal portion of arms. Proximal portion of the arms covered by skin and three or four (rarely five) club-shaped tubercles, ca. 170-340 µm long, on each lateral bar ( Fig. 6H ). Tubercles gradually decrease in size and number distally, becoming absent near arm tips ( Fig. 6I ). Entire oral surface of arms covered by skin ( Fig. 6J ). First to third tentacle pores lacking arm spines; fourth pore with two (rarely one or three) arm spines ( Fig. 6J ). All arm spines on each tentacle pore subequal throughout arms ( Fig. 6J, K ). In proximal third of arms, arm spines ovoid and minute ( Fig. 6J ), ca. one-third to two-thirds as long as corresponding arm segment ( Fig. 6J ). In middle of arms, arm spines club-shaped, as long as corresponding arm segment. In distal third of arms, arm spines hook-shaped, as long as corresponding arm segment ( Fig. 6K ). Lateral arm plates concealed by skin.

COLOUR. McKnight (2003) described the colour of the holotype as “In ethanol, areas between radial shields as well as dorsal surfaces of arms light brown, rest of body creamy-white”. However, by our observation, the holotype is uniformly creamy white. The colour might be diluted in long term ethanol preservation. Colour in life is unknown.

Distribution

Only known from off Cook island, 417-446 m depth, New Zealand (type locality, McKnight 2003).

Remarks

Asterostegus maini is related to A. tuberculatus in sharing relatively small tubercles and multiple oral interradial plates on each interradius, while A. sabineae possess relatively large tubercles and only one oral interradial plate.

Asterostegus maini and A. tuberculatus can be distinguished by the size and arrangement of tubercles on the disc, the number of tubercles on lateral bars, and the number and arrangement of oral interradial plates ( Table 1 , see also remarks for A. sabineae ).

Figures

Fig. 6. Asterostegus maini McKnight, 2003 (NIWA 7564, H-733). A. Aboral view. B. Oral view. C. Aboral periphery of disc. D. Aboral central disc. E. Jaws. F. Oral periphery of disc. G. Lateral disc. H. Aboral proximal portion of arm. I. Aboral middle portion of arm. J. Oral proximal portion of arm. K. Lateral middle portion of arm. Arrows indicate positions where oral interradial plates should exist (F, G). Abbreviations: ADS = adoral shield, AS = arm spine, GS = genital slit, LAP = lateral arm plate, Te = teeth, Ten = tentacle, Tu = tubercle.