Astrocladus socotrana Baker & Okanishi & Pawson 2018, sp. nov.
Creators: name: Baker, Alan N.
name: Okanishi, Masanori
name: Pawson, David L.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Ophiuroidea
Euryalida
Gorgonocephalidae
Astrocladus
Astrocladus socotrana

description: Astrocladus socotrana sp. nov.
(Figs. 12–16)
Material Examined. Holotype: USNM 1072535, Anton Bruun Cruise 9 Station 465, south of Socotra Island, 11°37’N, 51°27’E, 67–72 m, 18 December 1964, 1 specimen, disc diameter 21 mm (Fig. 11–15). Paratypes: USNM 1072536, Anton Bruun Cruise 9 Station 463, south of Socotra Island, 11°24’N, 51°35’E, 75–175 m, 17 December 1964, 2 specimens, disc diameter 32 mm (Figure 3B) and 33 mm. USNM 1201811, same locality data as Holotype, 1 specimen, disc diameter 12 mm.
Etymology. The specific name refers to the type locality, which is also mountainous, like the aboral surface of this species.
Diagnosis. Disc closely covered with tall conical tubercles with smooth rounded apices; proximal aboral and lateral surfaces of arms with similar but smaller tubercles. Oral arm surfaces covered with flat polygonal plates with slightly raised sutures. Arms with six or seven branches.
Description of holotype. External morphology. Radial shields, center of disc, and interradial areas covered with prominent cone-shaped tubercles with smooth tops lacking any glassy spines (Figs. 12A, C, 13A–B, E). Largest tubercles tall (<3.2 mm high), on and obscuring radial shields, becoming smaller centrally where the disc is deeply depressed (Fig. 13A–B). Genital slits bordered by minute papillae each with one fine glassy terminal point (Fig. 13D). Oral papillae clustered at proximal tip of jaw, absent distally (Fig. 13C). One madreporite at a margin of an interradius.
Five branching arms, up to 120 mm long, tightly coiled (Fig. 12A–B). First branch at disc margin, thereafter bifurcating 6–7 times. Aboral and lateral surfaces of arms out to between third and fourth branches with scattered tubercles similar to, but smaller than, those on disc (Fig. 13D–E). Distal arm surfaces with dense covering of circular, raised granules (Fig. 14A). Oral surfaces of arms covered with flat polygonal plates with slightly raised sutures (Fig. 14B–D). Six arm segments to first arm fork at disc margin, five to second fork.
Arm spines present from adjacent to first arm fork (Fig. 14B), four spines throughout arm (Fig. 14B–E), spines initially simple on proximal segments, developing a glassy terminal point and three secondary points distally. Discontinuous girdle bands on arms from disc margin, becoming continuous before the third fork (Figs. 13D–E, 14A).
Ossicle morphology. All vertebrae with hourglass-shaped streptospondylous articulations (Fig. 15C–D, F–G). Surfaces of lateral and aboral furrows with tubercles on basal portion of the arm (Fig. 15B). Depressions for tube feet openings in the distal part of oral-lateral side of vertebrae (Fig. 15A, E). A pair of radial water canals opening on the oral groove of vertebrae, near depression of the tube feet (Fig. 15A, E). Tubercles on basal portion of the arms with smooth rounded apices (Fig. 15I). Hooklet-bearing plates possessing approximately 12 tubercle-shaped articulations for hooklets in the basal portion of the arm (Fig. 15J), approximately 8 articulations in the distal portion (Fig. 15K). The articulations form two parallel rows (Fig. 15J, K). Each hooklet bearing one inner tooth (Fig. 16A–B). Lateral arm plates long, bar like, with straight distal edge and concave basal edge (Fig. 16C, E). On basal portion of arm, lateral arm plates with a perforation on inner side and pairs of simple nerve and muscle openings on oral-external side (Fig. 16C–E) and on distal portion of the arms, two nerve openings besides the dorsal lobe and three articulations for hooklets on oral surfaces (Fig. 16F). No perforation visible on inner side (Fig. 16G). Arm spines on the basal portion of the arm ovoid and having three secondary points, approximately one-seventh length of the height of the spine (Fig. 16H). Distally, the arm spines transformed into hooks with two or three inner teeth, respectively (Fig. 16I). The hook-shaped arm spines distinguished from hooklets on aboral and lateral surface of the arm by lacking reticular structure (Fig. 16A–B, I).
Remarks. Astrocladus socotrana sp. nov. is remarkable for its dense covering of prominent, smooth disc and arm tubercles, which distinguish it from its closest congeners, such as A. exiguus and A. euryale, which have reduced tuberculation, mostly on the radial shields.
Distribution. Known only from type locality, south of Socotra, northern Indian Ocean, 62– 175 m.
description: Published as part of Baker, Alan N., Okanishi, Masanori & Pawson, David L., 2018, Euryalid brittle stars from the International Indian Ocean Expedition 1963 - 64 (Echinodermata: Ophiuroidea: Euryalida), pp. 1-27 in Zootaxa 4392 (1) on pages 16-20, DOI: 10.11646/zootaxa.4392.1.1, http://zenodo.org/record/1194434