Asterostegus tuberculatus Mortensen 1933
Creators: name: Okanishi, Masanori
name: Fujita, Toshihiko
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Euryalida
Euryalidae
Asterostegus
Asterostegus tuberculatus

description: Asterostegus tuberculatus Mortensen, 1933
Figs 7-10
Asterostegus tuberculatus Mortensen, 1933: 298-300, figs 24-25, pl. 19; figs 4-5.
Asterostegus tuberculatus – Okanishi & Fujita 2013: 568, 572, 575, fig. 1, tables 2-3.
Diagnosis
Tubercles present on periphery of radial shields as well as interradial periphery of disc, ca. 350 µm long. On proximal portion of arm, two or three tubercles on top of each lateral bar. Five to eight oral interradial plates forming two rows.
Material examined
SMNH-123461, one ethanol preserved specimen, west coast of Reunion Island, 500 m, 2009.
Description
MEASUREMENTS. SMNH-123461: disc diameter 14.5 mm, arm length 259 mm.
DISC. Disc circular in shape, with notched interradial edges (Fig. 7A). On aboral surface, radial shields and their surrounds tumid (Fig. 7A). Disc surface covered by skin and evenly scattered tubercles (Fig. 7A-C). Tubercles on disc center granule-shaped, ca. 300 µm diameter and 400 µm height (Fig. 7C) and on periphery club-shaped tubercles, ca. 350 µm diameter and 550 µm height (Fig. 7B). Radial shields, ca. 7.5 mm long and 0.7-2.0 mm wide (Fig. 7A), completely covered by skin and tubercles. Oral surface of the disc covered by skin and granule-shaped external ossicles, ca. 120-240 µm diameter, which are evenly scattered (Fig. 7D, F). Four spearhead-shaped teeth form a vertical row on dental plate (Fig. 7E). Six to seven domed oral papillae lie on each side of jaw (Fig. 7E). Adoral shields somewhat hexagonal-shaped (Fig. 7F). Oral interradial plates pentagonal or hexagonal-shaped, in two rows (Fig. 7G). Proximal row consists of two oral interradial plates, distal row consists of three interradial plates (Fig. 7G). Lateral interradial surface of disc nearly vertical, covered entirely by skin (Fig. 7H). Two genital slits in each interradius, 4.1 mm long and 0.7 mm wide (Fig. 7H). One madreporite present between oral side of genital slits (Fig. 7H).
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 arms 6.85 mm wide and 5.5 mm high, oblong in cross-section. Aboral surface arched and oral surface flattened from middle to distal portion of arms. Proximal portion of arms covered by skin and two or three club-shaped tubercles, ca. 400 µm long and 750 µm height (Figs 7I; 8J-K), on each lateral bar. On middle portion of arms, tubercles granule-shaped, ca. 450 µm long (Fig. 9A), one or two on each lateral bar. On oral surface, four to five granule-shaped external ossicles, scattered on each arm segment, ca. 150-300 µm long on proximal portion of arms (Fig. 9C) and ca. 100-150 µm long on middle portion of the arms (Fig. 9D). Tubercles and external ossicles on oral surface gradually decrease in size distally, becoming absent near arm tips (Fig. 9B, E-F). First to third tentacle pores lacking arm spines; two arm spines from fourth pore (Fig. 7D). In proximal third of arms, arm spines ovoid and minute (Figs 8G; 9C). Outer arm spines ca. two-thirds as long as corresponding arm segment, inner arm spines slightly shorter, ca. two-thirds as long as outer spine (Fig. 9C). In middle of arm, arm spines club-shaped (Figs 8H; 9D). Inner and outer arm spines of equal length, ca. half as long as corresponding arm segment (Fig. 9D). In distal third of arms, arm spines hook-shaped with smooth lamina on distal side (Fig. 9E). Inner and outer spines of equal length, ca. one-third as long as corresponding arm segment (Figs 8I; 9E-F). Lateral arm plates concealed by skin and external ossicles, with two pairs of muscle and nerve openings, and each of them associated with an arm spine articulation (Fig. 8A-F). Ventral lobes and dorsal lobes beside muscle openings meet (Fig. 8 C-D). A condyle present between each muscle and each nerve opening (Fig. 8C, D). Vertebrae with streptospondylous articulations (Fig. 10A, E), oral bridges on oral side (Fig. 10A, C, E, G), knobs on lateral side (Fig. 10B, D, F, H). These features indicate A. tuberculatus ’ affiliation to the family Euryalidae. Knobs on lateral side of vertebrae elongate throughout the arms (Fig. 10B, D, F, H).
COLOUR. Uniformly white, slightly grayish on aboral disc surface except radial shields (Fig. 7A). Black spots appear on aboral and lateral arms randomly, every 2-20 arm segments (Fig. 7I). Colour in life is unknown.
Distribution
Off Durban, 376 m depth, Republic of South Africa (type locality, Mortensen 1933b). Off Reunion Island, 500 m depth (present study).
Remarks
Asterostegus tuberculatus can be distinguished from the other two species in the arrangement of tubercles on the disc, numbers of tubercles on lateral bars, and the arrangement of oral interradial plates (Table 1, see also the Remarks for the other two species).
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 12-17, DOI: 10.5852/ejt.2014.76, http://zenodo.org/record/3835020