Tethyaster grandis (Verrill 1899)

Tethyaster grandis (Verrill)

Sideriaster grandis Verrill, 1899:220, pl. 30: figs. 8–8b; 1914:21; 1915:192, pl. 12: figs. 5, 5b.

Tethyaster grandis.–Clark and Clark, 1954:17, fig. 1b, pls. 11, 12.

This stellate species has a large disc and five broadly based arms which taper evenly to a moderately acute point. Both actinal and abactinal surfaces are extremely plane and even, the only height being defined by the marginals. The dorsal paxillae are less than twice as high as wide and arise from a lobed base to a rounded top which bears 3–8 granuliform central spinules and about a dozen longer peripheral spinules. The high, narrow superomarginals, confined mostly to the sides of the rays, are densely covered with granules which become small and spiniform at the deep interplate fascioles. The inferomarginals, of similar size and shape, bear three or more large, flattened lanceolate spines and many small flattened spinules. The actinal interradial areas are large, with large sub-paxilliform plates in regular rows (there are frequently a few odd interradial actinals just below the jaw). They are covered with large granules and small peripheral spinules, and a single row extends nearly to the end of the arm. The adambulacral plates project slightly into the furrow and bear three flattened furrow spines, the central one at right angles to the groove and the other two nearly parallel to it. Behind, on the actinal face of the plate, are 3 or 4 stouter truncate spines, and behind them are a few much smaller spines and frequently 1 or 2 stout, short, three-valved pedicellariae. The mouth plates are slightly raised above the actinal surface and bear many stout granuliform spinules, with a cluster of stout truncate spines at the apex. In many specimens, three-or four-valved pedicellariae are scattered all over the actinal surface. The tube feet are small and pointed. The madreporite is large and flat, with shallow radiating gyri.

JUVENILES.–Young specimens of Tethyaster differ from the adults in that the marginals extend more onto the dorsal surface, the spines are not developed on the inferomarginals, the madreporite is small and nearly concealed by paxillae, and the adambulacral furrow spines are not flattened and are more palmate.

Known previously only from the Gulf of Mexico, this species has a depth range of 35–162 fathoms.

MATERIAL EXAMINED.–Silver Bay Station 5106 (3) [R=16 mm, r=7 mm, Rr=1:2]. Oregon Stations: 5913 (3) [R=18 mm, r=6 mm, Rr=1:3]; 3621, 1. Oregon II Station 10559 (1) [R=82 mm, r=21 mm, Rr=1:4]. Alaminos Stations: 13/64–A–10 (1) [R=105 mm, r=31 mm, Rr=1:3]; 5/68–A–13, 2.

Other Species of Tethyaster

Tethyaster vestitus, the other species falling within the scope of this report, bears a large flat spine on the actinal plates, and the inferomarginal spines are broadly truncate, rather than sharp pointed. It ranges from 08° to 40° north, and apparently does not occur east of 75° west. Its depth range is 44–146 fathoms.

Dipsacaster Alcock

Dipsacaster Alcock. 1893a:87; 1893b: 172. [Type, by original designation, D. sladeni Alcock.]

Rays five; form depressed, disc broad, with well-developed actinal interradial areas; marginal plates large; inferomarginals broader than superomarginals with tuft of spines at outer edge; superomarginals sometimes with 1–3 small tubercles; paxillae with round or stellate base, tall pedicel crowned with tuft of many small, crowded, erect spinelets; papulae all over abactinal surface, 5 or 6 around each plate; actinal intermediates bearing paxilliform group of spinules; fasciolar channels from inferomarginals to adambulacrals; adambulacrals with palmate or pectinate cylindrical or compressed furrow spines, smaller spinelets on actinal face; mouth plates prominent, broad, with numerous spinules; madreporite large, hidden by paxillae; tube feet pointed.