Asterostegus sabineae, Okanishi & Fujita, 2014

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 : 4-9

publication ID	https://doi.org/ 10.5852/ejt.2014.76
publication LSID	lsid:zoobank.org:pub:01BEFFB2-2E53-4B1E-A7BC-36702313BBF8
DOI	https://doi.org/10.5281/zenodo.3851753
persistent identifier	https://treatment.plazi.org/id/03917D3B-D907-F77A-B76B-7834FD470935
treatment provided by	Tatiana
scientific name	Asterostegus sabineae
status	sp. nov.

Treatment

Asterostegus sabineae View in CoL sp. nov.

urn:lsid:zoobank.org:act:D2F3C5E4-B56D-4726-A7B7-FDB56A85B95F

Figs 2-5 View Fig View Fig View Fig View Fig

Asterostegus sp. – Okanishi & Fujita 2013: 568, 575, fig. 1, table 1.

Diagnosis

Tubercles ca. 1-1.2 mm long cover entire radial shields. On proximal portion of arm, one (rarely two) tubercle on each lateral bar. One oral interradial plate present on each interradius.

Etymology

The specific name is for Dr. Sabine Stöhr of the Swedish Museum of Natural History, eminent Swedish researcher of the Ophiuroidea.

Type material

MADAGASCAR: Holotype ( MNHN IE-2013-8012 ), three paratypes (SMNH-Type-8333) and one paratype (SMNH-Type-85436), all ethanol preserved specimens, off Madagascar, South Cape, Sainte Marie, 26˚16.35’S, 45˚10.45’E, 409-473 m, 14 May 2010, collected during the cruise Atimo Vatae 2010, St. CP3616.

Description

MEASUREMENTS. Holotype (MNHN IE-2013-8012): disc diameter 11.7 mm, arm length 118 mm. One paratype (SMNH-Type-8536): disc diameter 13.3 mm, arm length at least 55.4 mm (arms convoluted). DISC. Disc circular in shape. Radial shields and their surrounds tumid ( Fig. 2A View Fig ). Aboral surface of disc covered by skin and two to four domed tubercles in a line on each radial shield ( Fig. 2A-C View Fig ). Tubercles ca. 1.0- 1.2 mm long on disc periphery, ca. 0.8 mm long at disc center ( Fig. 2B View Fig ). Radial shields, ca. 7.5 mm long, 0.7-2.7 mm wide, completely covered by skin and tubercles ( Fig. 2B-C View Fig ). Oral surface of disc covered by skin ( Fig. 2D-E View Fig ). More than three triangular teeth form vertical row on dental plate ( Fig. 2E View Fig ). One oral interradial plate present on distal side of adoral shield ( Fig. 2H View Fig ). Lateral interradial surface of disc nearly vertical, covered by skin and granule-shaped external ossicles, ca. 150-400 µm long ( Fig. 2H View Fig ). Two genital slits in each interradius, 3.0 mm long and 0.4 mm wide ( Fig. 2H View Fig ). One madreporite present on distal side of oral interradial plate ( Fig. 2H View Fig ).

ARMS. Arms simple, five in number, with no abrupt gap in width due to presence of gonads in proximal portion of arms ( Figs 2A View Fig ; 3A View Fig ). Arms tapering gradually distally. Proximal portion of arms 3.0 mm wide and 3.7 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 one (rarely two) domed tubercles, ca. 1.0- 1.3 mm long ( Fig. 3A View Fig ), on each lateral bar. If two tubercles present on lateral bar, both are smaller, ca. 800 µm long ( Fig. 3A View Fig ). From middle to distal portion of arms, tubercles gradually decrease in size distally, becoming absent near arm tips ( Fig. 3B-C View Fig ). Oral surface of arms covered by skin ( Fig. 3D-E View Fig ). First to third tentacle pores lacking arm spines; two arm spines from fourth pore ( Fig. 2F View Fig ). In proximal third of arms, outer arm spines ca. one quarter to half as long as corresponding arm segment, and inner arm spines slightly shorter than outer spines ( Figs 2F View Fig ; 3D View Fig ). In middle of arms inner and outer arm spines subequal, ca. two-thirds as long as corresponding arm segment ( Fig. 3D View Fig ). In distal third of arms, arm spines hook-shaped ( Fig. 3F View Fig ). Inner and outer spines subequal, ca. two-thirds as long as corresponding arm segment ( Fig. 3C, E-F View Fig ). Lateral arm plates concealed by skin and visible at distal arm tips where skin becomes thinner ( Fig. 3E View Fig ).

COLOUR. Body creamy white, arm spines brown ( Figs 2A, G, H View Fig ; 3B, D View Fig ). Colour in life is unknown.

OSSICLE MORPHOLOGY. Ossicles separated from one paratype, SMNH-Type-8536. Vertebrae. Vertebrae with streptospondylous articulations ( Fig. 4A, E View Fig ), oral bridges on oral side ( Fig. 4C, G View Fig ) and knobs on lateral side ( Fig. 4D, H View Fig ), and not inclining from proximal-aboral side to distal-oral side of arms ( Fig. 4B, D, F, H View Fig ) throughout the arms. These features indicate the new species’ affiliation to the family Euryalidae . Knobs on proximal portion of arms elongated, becoming rounded toward distal portion of arms ( Fig. 4D, H View Fig ).

LATERAL ARM PLATES. Lateral arm plates in middle portion of arms with two pairs of muscle and nerve openings, each of them associated with arm spine articulation ( Figs 4I View Fig , 5A-C View Fig ). Dorsal and ventral lobes beside muscle openings contact each other, a tubercle structure present between each muscle and nerve opening ( Figs 4I View Fig , 5A View Fig ). Arm spines club-shaped, both 650 µm long and wide on proximal portion of arms ( Fig. 5D View Fig ), 450 µm long and 500 µm wide on middle portion of arms ( Fig. 5E View Fig ), hook-shaped, ca. 230 µm long on distal portion of arms, with one secondary tooth and smooth lamina on proximal portion ( Fig. 5F View Fig ).

Distribution

Only known from off Madagascar, 409-473 m depth (type locality, present study).

Remarks

The new species falls within Asterostegus by virtue of having simple arms, tubercles on radial shields and aboral arms, oral interradial plates, triangular teeth and granule-shaped oral papillae, an oral bridge on oral side of vertebrae, and smooth lamina of distal arm spines ( Fell 1960; McKnight 2003).

Asterostegus sabineae sp. nov. can be distinguished from the other two species as follows: two to four tubercles on the radial shields of the present new species form a line on each radial shield ( Fig. 2A View Fig ), whereas the tubercles of A. maini number ca. 10 and are scattered on the periphery of the radial shields only ( Fig. 6C View Fig ). Those of A. tuberculatus number 5-15 and are scattered over the entire radial shields as well as on the interradial areas and periphery of the aboral disc ( Fig. 7A View Fig ). The size of tubercles of the new species on the periphery of the radial shield is ca. 1.0- 1.2 mm long ( Fig. 2B View Fig ). In contrast, those of A. maini and A. tuberculatus in the same position are ca. 250-300 µm ( Fig. 6C View Fig ) and ca. 350 µm long ( Fig. 7A View Fig ), respectively.

The new species has one or two tubercles on the top of each lateral bar in the arms proximally ( Fig. 2H View Fig ), while A. maini and A. tuberculatus have three to five ( Fig. 6H View Fig ), and two to three tubercles ( Fig. 7I View Fig ), respectively.

The number of oral interradial plates of the new species is one on each interradius ( Fig. 3F View Fig ) while there are three to five plates in A. maini ( McKnight 2003) and five to eight in A. tuberculatus ( Fig. 7G View Fig ) ( Mortensen 1933b). The oral interradial plates of the latter two species form rows (see also the description of A. tuberculatus ) ( McKnight 2003).