Asterostegus sabineae Okanishi & Fujita 2014, sp. nov.
Creators: name: Okanishi, Masanori
name: Fujita, Toshihiko
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Euryalida
Euryalidae
Asterostegus
Asterostegus sabineae

description: Asterostegus sabineae sp. nov.
urn:lsid:zoobank.org:act: D2F3C5E4-B56D-4726-A7B7-FDB56A85B95F
Figs 2-5
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). Aboral surface of disc covered by skin and two to four domed tubercles in a line on each radial shield (Fig. 2A-C). Tubercles ca. 1.0- 1.2 mm long on disc periphery, ca. 0.8 mm long at disc center (Fig. 2B). Radial shields, ca. 7.5 mm long, 0.7-2.7 mm wide, completely covered by skin and tubercles (Fig. 2B-C). Oral surface of disc covered by skin (Fig. 2D-E). More than three triangular teeth form vertical row on dental plate (Fig. 2E). One oral interradial plate present on distal side of adoral shield (Fig. 2H). Lateral interradial surface of disc nearly vertical, covered by skin and granule-shaped external ossicles, ca. 150-400 µm long (Fig. 2H). Two genital slits in each interradius, 3.0 mm long and 0.4 mm wide (Fig. 2H). One madreporite present on distal side of oral interradial plate (Fig. 2H).
ARMS. Arms simple, five in number, with no abrupt gap in width due to presence of gonads in proximal portion of arms (Figs 2A; 3A). 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), on each lateral bar. If two tubercles present on lateral bar, both are smaller, ca. 800 µm long (Fig. 3A). From middle to distal portion of arms, tubercles gradually decrease in size distally, becoming absent near arm tips (Fig. 3B-C). Oral surface of arms covered by skin (Fig. 3D-E). First to third tentacle pores lacking arm spines; two arm spines from fourth pore (Fig. 2F). 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; 3D). In middle of arms inner and outer arm spines subequal, ca. two-thirds as long as corresponding arm segment (Fig. 3D). In distal third of arms, arm spines hook-shaped (Fig. 3F). Inner and outer spines subequal, ca. two-thirds as long as corresponding arm segment (Fig. 3C, E-F). Lateral arm plates concealed by skin and visible at distal arm tips where skin becomes thinner (Fig. 3E).
COLOUR. Body creamy white, arm spines brown (Figs 2A, G, H; 3B, D). Colour in life is unknown.
OSSICLE MORPHOLOGY. Ossicles separated from one paratype, SMNH-Type-8536. Vertebrae. Vertebrae with streptospondylous articulations (Fig. 4A, E), oral bridges on oral side (Fig. 4C, G) and knobs on lateral side (Fig. 4D, H), and not inclining from proximal-aboral side to distal-oral side of arms (Fig. 4B, D, F, H) 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).
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, 5A-C). Dorsal and ventral lobes beside muscle openings contact each other, a tubercle structure present between each muscle and nerve opening (Figs 4I, 5A). Arm spines club-shaped, both 650 µm long and wide on proximal portion of arms (Fig. 5D), 450 µm long and 500 µm wide on middle portion of arms (Fig. 5E), hook-shaped, ca. 230 µm long on distal portion of arms, with one secondary tooth and smooth lamina on proximal portion (Fig. 5F).
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), whereas the tubercles of A. maini number ca. 10 and are scattered on the periphery of the radial shields only (Fig. 6C). 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). 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). In contrast, those of A. maini and A. tuberculatus in the same position are ca. 250-300 µm (Fig. 6C) and ca. 350 µm long (Fig. 7A), respectively.
The new species has one or two tubercles on the top of each lateral bar in the arms proximally (Fig. 2H), while A. maini and A. tuberculatus have three to five (Fig. 6H), and two to three tubercles (Fig. 7I), respectively.
The number of oral interradial plates of the new species is one on each interradius (Fig. 3F) while there are three to five plates in A. maini (McKnight 2003) and five to eight in A. tuberculatus (Fig. 7G) (Mortensen 1933b). The oral interradial plates of the latter two species form rows (see also the description of A. tuberculatus) (McKnight 2003).
description: Published as part of Okanishi, Masanori & Fujita, Toshihiko, 2014, A taxonomic review of the genus Asterostegus (Echinodermata: Ophiuroidea), with the description of a new species, pp. 1-18 in European Journal of Taxonomy 76 (76) on pages 4-9, DOI: 10.5852/ejt.2014.76, http://zenodo.org/record/3835020