[In this family,]the disc is small in relation to the arms, which are long, narrow and cylindrical. The aboral plates are arranged as a fine or coarse mesh, usually bearing short spines, alone or in groups. No pedicellariae. The tube feet have single ampullae.
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Henricia asthenactis has a meshlike aboral surface with a single row of 2 to 4 flesh-covered, well-spaced spinelets on the ridges of each plate. The areas between the ridges have about 10 papulae. In alcohol, specimens are yellowish-white. The five arms are up to 11 cm long, and the arm-to-disc ratio is from 4.4 to 6.6. There is a regular series of supero- and inferomarginals with spinelets on each plate and a few intermarginals with 1 or 2 spinelets, at the base of each arm. The oral intermediates form a short series proximally. The adambulacrals have a transverse series of 3 to 5 spines, the proximal spine being longer than the width of the plate, and there is a small knob like spinelet deep inside the furrow.
Characteristics
Similar Species
The aboral surface of Henricia asthenactis resembles H. aspera aspera, but the arms are shorter relative to the disc and the spinelets on the ridges are larger.
Kamchatka, the Shumagin Islands, the Bering Sea to Santa Barbara Island, California and Gulf of California. Found on mud, sand or gravel at depths of 91 to 1250 metres. Rare in this region (the area from Glacier Bay to Puget Sound to a depth to 200 metres).
