Astrocyclus somaliensis, 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 : 20-22

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.5958811
persistent identifier	https://treatment.plazi.org/id/03D88782-FFCF-FFBD-7896-FCF5675BFD0B
treatment provided by	Plazi
scientific name	Astrocyclus somaliensis
status	sp. nov.

Treatment

Astrocyclus somaliensis View in CoL sp. nov.

( Figs. 17A–C View FIGURE 17 , 18–21 View FIGURE 18 View FIGURE 19 View FIGURE 20 View FIGURE 21 )

Material Examined. Holotype: USNM 1411388 Anton Bruun station 9–463, 11˚ 24’ N, 51˚ 35’ E, 75–175 m, 18 December 1964, off the north-eastern coast of Somalia, 1 specimen, disc diameter 27 mm ( Fig. 16 View FIGURE 16 ). Paratypes: USNM 1422067, same locality data as holotype, 3 specimens, disc diameter 24, 16 and 10 mm.

Etymology. The specific name refers to the collection locality.

Diagnosis. Astrocyclus with aboral surface of disc depressed centrally, radial shields converging at center. Radial shields partly covered with more or less continuous transverse thin white lines made up of closely packed granules (6–8/mm), which loop over the shields and partly extend into the inter-shield and interradial areas.

Description of the holotype. External morphology. The disc five-lobed, 27 mm in disc diameter, with arms at least 115 mm long ( Fig. 17A–B View FIGURE 17 ). The disc markedly depressed centrally ( Fig. 18A View FIGURE 18 ); narrow, raised, radial shields converging there ( Fig. 18A–B View FIGURE 18 ). The entire aboral surface, including the area between each of the radial shields, covered with evenly spaced low granules ( Fig. 18A–B View FIGURE 18 ). The radial shields partly covered with more or less continuous transverse white lines made up of microscopic, closely packed granules (6–8/mm), which loop over the radial shields, with some partly extending into the inter-shield and inter-radial areas of the disc. The arm segments are conspicuously ringed laterally and aborally by narrow bands of microscopic granules, mostly in two rows, which stand out from the surface ( Fig. 19B–D View FIGURE 19 ). There are two, then three, small arm spines with hyaline tips per segment ( Fig. 18D–F View FIGURE 18 ). The distalmost arm segments have girdle bands, with strongly curved hyaline hooklets ( Fig. 19D View FIGURE 19 ). The oral surface of the arms and disc are covered with evenly spaced granules, and there is one madreporite in each of the five interradial disc areas, jaws entirely covered by spiniform teeth and oral papillae ( Fig. 18C View FIGURE 18 ).

Ossicle morphology. All vertebrae with hourglass-shaped streptospondylous articulations ( Fig. 20C–D, G–H View FIGURE 20 ). Surfaces of lateral and aboral furrows smooth, without ornamentations ( Fig. 20A–B, E–F View FIGURE 20 ). Depressions for tube feet openings in the distal part of oral-lateral side of vertebrae ( Fig. 20A, F View FIGURE 20 ). A pair of radial water and nerve canals opening on the oral groove of vertebrae on basal portion of the arm ( Fig. 20A View FIGURE 20 ) but radial nerve canals invisible on distal portion of the arm ( Fig. 20F View FIGURE 20 ). Lateral arm plates long, bar-like, with straight basal edge and concave distal edge ( Fig. 20I –J View FIGURE 20 ). On basal portion of arm, perforation invisible on aboral side and pairs of simple nerve openings on oral-external side ( Figs. 20J View FIGURE 20 , 21A View FIGURE 21 ). Hooklet-bearing plates possessing tubercle-shaped articulations for hooklets, approximately 7 on distal portion of the arm ( Fig. 21B View FIGURE 21 ). The articulations forming two parallel rows ( Fig. 21B View FIGURE 21 ). Each hooklet without inner teeth ( Fig. 21G–H View FIGURE 21 ). Arm spines in the basal portion of the arm ovoid, with one or two secondary points ( Fig. 21D–E View FIGURE 21 ). In the distal portion, the arm spines transformed into hooks with one inner teeth ( Fig. 21F View FIGURE 21 ). The hook-shaped arm spines distinguished from hooklets on aboral and lateral surface of the arm by lacking reticular structure ( Fig. 21F–H View FIGURE 21 ).

Variation. In the smallest specimen (USNM 1422067, dd. 10 mm), the entire area between the shields is covered with transverse lines. This feature differs from that in the Brazilian samples described and illustrated by Gondim et al (2014), where between each radial shield there are 6–7 discrete groups of granules running in line with the shields ( Fig. 17D View FIGURE 17 ). In the two larger specimens (USNM 1411388, dd. 27 mm; USNM 142 2067, dd. 24 mm), a few of these lines of granules extend between the shields.

Remarks. As all four examined specimens from the Indian Ocean have similar disc and radial shield coverings which differ markedly from the western Atlantic specimens, we consider that they represent a separate taxon, which we here establish as a new species. The arms bifurcate at least 15 times, the first branch within the diameter of the disc, and the second at the distal end of the radial shields ( Fig. 17A–B View FIGURE 17 ).

Astrocyclus caecilia has been recorded from the Caribbean Sea, Gulf of Mexico (type locality), and from northeastern Brazil by Gondim et al. (2014), who have illustrated the species extensively. The vast geographical separation of the type species and the Somalian form, plus the obvious morphological difference in the covering of the radial shields and their interradial aboral areas, indicate that a new species, Astrocyclus somaliensis sp. nov. should be erected for this Somalian form.