Solaster hexactis, Clark, Roger N. & Jewett, Stephen C., 2011

Clark, Roger N. & Jewett, Stephen C., 2011, Three new sea stars (Asteroidea: Solasteridae & Pterasteridae) from the Aleutian Islands, Zootaxa 3051, pp. 1-13 : 2-5

Solaster hexactis sp. nov.

Figures 1 –7

Type locality: Alaska, Aleutian Islands, W of Buldir Island (52° 18.50 N, 175° 49.00 E), 325 m. Type material. Table 1 .

Description. Small six-rayed form, Holotype, R = 41 mm, r = 15 mm. R: r = 1:2.7 (range 1:1.7 to 1:2.7); disc relatively small, rays moderately long, tapering to rather blunt tips. Dorsal side ( Fig. 1 ) moderately inflated. Papular pores numerous, small, occurring singularly or in pairs; papulae rather small. Abactinal plates cruciform, imbricating; Pseudopaxillae relatively large, bearing 20–40 spinelets with thorny tips; Madreporite very small, only about twice as large as pseudopaxillae, radially grooved, surrounded and obscured by six pseudopaxillae ( Fig. 2 ). Superomarginals only slightly larger than aboral pseudopaxillae. Inferomarginal plates about three to four times as wide as long, spaced about one half length apart, and usually slightly off set from the adjacent supramarginal; fan shaped, bearing about 50+ spinelets. Ventral side flattened; Oral interradial areas relatively wide, and bearing 40– 65 overlapping oblong plates with short pseudopaxillae bearing five to eight spinelets; synactinal series extending about one fifth of ray length. Adambulacral plates ( Fig. 3 ) about four times as wide as long, slightly curved, and slightly tapering distally, spaced a little more than one length apart; bearing a bristling curved actinal series of six to eight (five in very small, <R 10 mm specimens) moderately long, stout, tapering, membrane covered spines of about equal length, the tips of which are thorny, and a furrow series of two (one in very small, <R 10 mm specimens) long, slender, tapering, membrane covered spines, webbed at the base; base of spines rather bulbous. Paired oral plates ( Fig. 4 ) shovel-shaped, each bearing five to seven long, slender, membrane covered marginal spines, webbed at the base, with thorny tips, and four to eight (normally seven) short, slender, un-webbed sub oral spines. Living color of shallow-water specimens dull red (Fig. 5), deep-water specimens are uniformly white or pale tan, oral side cream.

FIGURE 5. Solaster hexactis sp. nov. Paratype (LACM 2007-123.001). Live, in. situ., Umak Island, 8 m; image: Héloïse Chenelot, 14 July, 2007. R = approximately 2.5 cm.

Distribution. Aleutian Islands (Fig. 7), from West of Buldir Island, (175°49 E) to Seguam Pass (172º40 W).

Habitat. Occurs at depths of 8–384 m, on black sand, gravel, cobble and pebbly bottoms. In shallow water, it may be found on the undersides of loosely piled cobbles or on the coralline algae (Clathromophum nereostratum & Lithothamnion spp.) covered bedrock, with bottom temperatures of 4.2–6.0°C.

Etymology. From the Greek hex meaning six, in reference to the number of rays.

Remarks. With its six rays, Solaster hexactis sp. nov. probably would not be confused with any of its congeners. All other known members of Solaster have seven (normally eight) to 15 rays. It could possibly be mistaken for a member of the Echinasteridae genus Henricia . However, it is easily distinguished by the armature of the adambulacral plates, which are obviously solasterid in form, with a single transverse row of actinal spines, and a single, horizontal row of two or more furrow spines. Very young specimens (<R 8 mm) of S. hexactis sp. nov. might be confused with another six-rayed solasterid (Gale et al. 2008), the tiny and rather similar appearing, Aleutiaster schefferi A. H. Clark, 1939 , but may be separated by the spination of the abactinal, oral, marginal and adambulacral plates.

Reproduction. On 18 July, 2004, a single brooding specimen ( Fig. 6) (LACM 2002-080.001) was trawled SSE of Seguam Island, at 169 m on a black sand substrate (leg. R. N. Clark, R/V Vesteraalen, 18 July, 2002). The specimen with an R of 1.4 cm contained eight tiny six-rayed juveniles (R = 1.0 mm) attached to the oral and proximal adambulacral region.

Solaster hexactis n. sp. is the first member of this genus found to brood its young under the disc, a behavior shared by several members of the echinasteriid genus Henricia , and the asteriid genus Leptasterias , but to our knowledge unknown amongst the Solasteridae .

FIGURE 7. Distribution map for Solaster hexactis sp. nov. (●); Solaster spectabilis sp. nov. (♦); Pteraster willsi sp. nov. (*).

Figures

FIGURES 1 – 4. Solaster hexactis sp. nov. Holotype (LACM 1997 - 168.008). Fig. 1, Whole animal, aboral view; bar = 2.0 cm. Fig. 2, Close-up, aboral surface (M = Madreporite); bar = 5.0 mm. Fig. 3, Adambulacral area; bar = 1.0 mm. Fig. 4, Close-up, oral region; 2.0 mm.

Tables

TABLE 1. Type material: Solaster hexactis sp. nov.

Type	Deposition & No. of Collection Site Specimens	Collection Depth, m	Collection Date	Collector & Method
Holotype	LACM 1997- W of Buldir Island 52°18.50 168.008, dry N, 175°49.00 E; NMFS 23-199701-243	325 m	9 August, 1997	R. N. Clark, trawled, R/V Dominator
Paratype	USNM 1153699 Petrel Bank 52°30.29 N, 1 specimen, dry 179°58.62 E; NMFS 23-199401-145	284-289 m	9 July, 1994	R. N. Clark, trawled, R/V Ve s t e r aa l e n