Hymenaster modestus Verrill 1885

Hymenaster modestus Verrill, 1885:151; 1894:277; 1895:203

This substellate form has a broad disc and five short, broad, petaloid arms. The dorsal membrane is thin and fragile and contains a few minute granular deposits. The paxillar abactinal plates are cruciform, with a moderately high pedicel that bears 3 or 4 long, slender spines, about twice the length of the pedicel. There are roughly five rows of plates on each arm. The spiraculae are numerous and small; larger holes in the membrane, which might be mistaken for large spiraculae, are tears in the dorsal membrane. These are present in every specimen I have seen, including the type. The osculum is large and has five valves of 6–14 long spines, evenly graded from the longest in the center of the valve to the shortest at the ends. These are webbed together throughout their length, and the valve is longer than the diameter of the osculum, so there is considerable overlap when the osculum is closed. The five ossicles supporting the valves are the most massive ossicles present, crescentic, with a short, sturdy pedicel broadly expanded at the top into a tumid, crescentic knob. The actinal surface is without deposits of any kind; the actinal tissue is supported by actinolateral spines of moderate length, and there is a naked interradial area.

The lateral fringe is wide and unsupported; in contracted specimens, however, the actinolateral spines may extend beyond the fringe. The ambulacral grooves are wide, with two rows of massive tube feet. The adambulacral plates bear three slender, subequal furrow spines. There are 15–25 actinolateral spines, of which the fifth to the seventh are the longest. The mouth plates are longer than wide, and each half bears a long, stout preoral spine, a similar suboral spine, and 3 or 4 smaller, more acute marginal spines, the outermost one of which might be considered a second suboral, as it sits slightly behind the line of the other 2 or 3 marginal spines. The aperture papillae are broad, flat, leaf shaped, and bear longitudinal ridges. They are borne on the adambulacral plates between the furrow spines and the actinolateral spine.

I have examined the type specimen of this species, and it is a juvenile, as indicated by the small size and the presence of several long spines at the terminus of the arms, in the position of the oculars, a juvenile character in most asteroids. Nevertheless, I have no hesitation in assigning the larger specimens below to the species H. modestus, thus extending the range of this species, previously reported as occurring from Nantucket to Cape Hatteras, in 1,098–1,451 fathoms.

MATERIAL EXAMINED.—Oregon Stations: 2821 (2) [R=30 mm, r=19 mm, Rr=1:1.1]; 2820 (3) [R=38 mm, r=23 mm, Rr=1:1.3].