Astrocladus socotrana, Baker & Okanishi & Pawson, 2018

Baker, Alan N., Okanishi, Masanori & Pawson, David L., 2018, Euryalid brittle stars from the International Indian Ocean Expedition 1963 - 64 (Echinodermata: Ophiuroidea: Euryalida), Zootaxa 4392 (1), pp. 1-27 : 16-20

publication ID	https://doi.org/ 10.11646/zootaxa.4392.1.1
publication LSID	lsid:zoobank.org:pub:B6A80A66-E868-4578-A5E5-655E0F18AA84
DOI	https://doi.org/10.5281/zenodo.5958807
persistent identifier	https://treatment.plazi.org/id/03D88782-FFD3-FFBB-7896-FF736025FD0A
treatment provided by	Plazi
scientific name	Astrocladus socotrana
status	sp. nov.

Treatment

Astrocladus socotrana View in CoL sp. nov.

( Figs. 12–16 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 View FIGURE 16 )

Material Examined. Holotype: USNM 1072535 View Materials , 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 View FIGURE 11 View FIGURE 12 View FIGURE 13 View FIGURE 14 View FIGURE 15 ) GoogleMaps . Paratypes: USNM 1072536 View Materials , 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 View FIGURE 3 ) and 33 mm GoogleMaps . USNM 1201811 View Materials , same locality data as Holotype, 1 specimen, disc diameter 12 mm. GoogleMaps

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 View FIGURE 12 , 13A–B, E View FIGURE 13 ). Largest tubercles tall (<3.2 mm high), on and obscuring radial shields, becoming smaller centrally where the disc is deeply depressed ( Fig. 13A–B View FIGURE 13 ). Genital slits bordered by minute papillae each with one fine glassy terminal point ( Fig. 13D View FIGURE 13 ). Oral papillae clustered at proximal tip of jaw, absent distally ( Fig. 13C View FIGURE 13 ). One madreporite at a margin of an interradius.

Five branching arms, up to 120 mm long, tightly coiled ( Fig. 12A–B View FIGURE 12 ). 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 View FIGURE 13 ). Distal arm surfaces with dense covering of circular, raised granules ( Fig. 14A View FIGURE 14 ). Oral surfaces of arms covered with flat polygonal plates with slightly raised sutures ( Fig. 14B–D View FIGURE 14 ). 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 View FIGURE 14 ), four spines throughout arm ( Fig. 14B–E View FIGURE 14 ), 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 View FIGURE 13 , 14A View FIGURE 14 ).

Ossicle morphology. All vertebrae with hourglass-shaped streptospondylous articulations ( Fig. 15C–D, F–G View FIGURE 15 ). Surfaces of lateral and aboral furrows with tubercles on basal portion of the arm ( Fig. 15B View FIGURE 15 ). Depressions for tube feet openings in the distal part of oral-lateral side of vertebrae ( Fig. 15A, E View FIGURE 15 ). A pair of radial water canals opening on the oral groove of vertebrae, near depression of the tube feet ( Fig. 15A, E View FIGURE 15 ). Tubercles on basal portion of the arms with smooth rounded apices ( Fig. 15I View FIGURE 15 ). Hooklet-bearing plates possessing approximately 12 tubercle-shaped articulations for hooklets in the basal portion of the arm ( Fig. 15J View FIGURE 15 ), approximately 8 articulations in the distal portion ( Fig. 15K View FIGURE 15 ). The articulations form two parallel rows ( Fig. 15J, K View FIGURE 15 ). Each hooklet bearing one inner tooth ( Fig. 16A–B View FIGURE 16 ). Lateral arm plates long, bar like, with straight distal edge and concave basal edge ( Fig. 16C, E View FIGURE 16 ). 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 View FIGURE 16 ) and on distal portion of the arms, two nerve openings besides the dorsal lobe and three articulations for hooklets on oral surfaces ( Fig. 16F View FIGURE 16 ). No perforation visible on inner side ( Fig. 16G View FIGURE 16 ). 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 View FIGURE 16 ). Distally, the arm spines transformed into hooks with two or three inner teeth, respectively ( Fig. 16I View FIGURE 16 ). The hook-shaped arm spines distinguished from hooklets on aboral and lateral surface of the arm by lacking reticular structure ( Fig. 16A–B, I View FIGURE 16 ).

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.