Figures 59–62 & 64
Type locality: Alaska, Aleutian Islands, Rat Islands, Rat Island (51 º 49.594 N, 178 º 27.184 E), 14 m. (AKALE 07-A0031).
Type material: Holotype, LACM 2007 -099.001; 1 Paratype, USNM 1125123 (leg. R.N. Clark, 1 July, 2007).
Diagnosis: Small moderately inflated, R to 2.3 cm, R:r 3–3.2; disc relatively broad, rays broad at base, tapering to slender tips; abactinal skeleton fine, open meshwork; pseudopaxillae round or oval, bearing 16–27 very slender spinules with 1–3 apical thorns. Actinal inter-radial series only about 75 % or R. Adambulacrals with 10–16 rather slender spines, in 3 rows, 2 long spines at the furrow edge, followed by 2 lateral rows of 3– 5, and a central row of 2–4. Color in life reddish, mottled with lighter colors.
Description: Small, moderately inflated, R to 2.3 cm (Holotype R = 2.1 cm), r to 0.7 cm, R:r 3–3.2 cm (Figs. 59 & 60); disc broad, rays relatively short, broad at base, tapering to slender tips. Abactinal plates small, round to oval, spaced about 1 diameter or so apart, giving a rather open reticulum; pseudopaxillae (Fig. 61) with 16–27 fairly long, even spinules, bearing 1–3 apical thorns; papular areas large, bearing 2–4 papulae each; madreporite small, round, spinose (spines often in broken ridges). Superomarginals twice or less the size of abactinal plates, bearing 12–17 long spinules; intermarginals limited to a few irregular plates at base of rays; inferomarginals less than twice as large as superomarginals, bearing 21–25 slender spinules in 2–3 rows. Adambulacrals (Fig. 62) with 1 fairly long, bent spine deep in furrow, 10–16 fairly long, stout actinal spines in 2 lateral rows of 3–6, and a (usually) partial central row of 2 –4, 1– 2 at edge of furrow much longer than others. Oral plates (Fig. 62) with 5 thick, bunt or pointed marginal and 6–9 similar sub-oral spines. Color in life (Fig. 64) reddish, often with lighter mottlings on abactinal surface, actinal surface yellow-cream.
Distribution: The three type specimens all were taken at Rat Island, mixed with the similar appearing H. tumida, but it is probably wide spread in the Aleutians.
Habitat: bedrock and boulders encrusted with coralline red algae, various sponges, hydroids and bryozoans.
Etymology: From the Latin, meaning small.
Remarks: This small species was taken mixed with the similar and very variable H. tumida (Figs. 63), from which it differs in 1) more open abactinal skeleton; 2) very slender abactinal spinules, those of H. tumida are very thick and blunt; 3) much more numerous (10–16) adambulacral spines, which occur in 3 rows in H. elachys, versus a single (often irregular or staggered) row of 4–8 in H. tumida (Fig. 63); and 4) smaller, more numerous papulae 2–4 per area versus usually 1, rarely 2, large papulae in H. tumida.