Hippasteria aleutica, Clark, Roger N. & Jewett, Stephen C., 2011

Clark, Roger N. & Jewett, Stephen C., 2011, A new sea star of the genus Hippasteria (Asteroidea: Goniasteridae) from the Aleutian Islands, Zootaxa 2963, pp. 48-54 : 49-52

Hippasteria aleutica sp. nov.

Figs. 1–7

Hippasteria sp. Barr & Barr, 1983: 175.

Type locality. Alaska, Aleutian Islands, Rat Island (51º 49.594 N 178º 27.184 E), 13 m, ( AKALE 07-A0031).

Type material.

Type Deposition Collection Location Collection Collection Date Collector & Method

Depth, m

Holotype LACM 2008 - 030.001 Rat Island 51 º 49.594 N, 13 June 8, 2008 R.N. Clark, scuba

1 specimen dry 178º 27.184 E, 13 m.

AKALE 07-A0031

Paratype USNM 1125124 Chuginadak Is 17 June 16, 2006 H. Chenelot, scuba

1 specimen dry 52° 48.289 N

169° 42.526 W

AKALE 06-0010

Paratype USNM E47392 Kiska Is 91 July 31, 1997 R.N. Clark, trawled

1 specimen dry 52° 04.17 N R/V Dominator 177° 15.20 E

NMFS 23-199701-199

Additional material.

Diagnosis. Large, broad, relatively rigid, R to 11 cm, R:r 1.7–1.8 ( Figs. 1–2 ); disc very broad, rays short, sharply tapering; abactinal and marginal plates surrounded by pointed granules or thorns, bearing relatively short, thick, blunt, cylindrical spines; abactinal surface also profusely covered with small, bivalve to quadravalve pedicellaria ( Fig. 3 ); adambulacral plates with two thick, blunt furrow spines, the adoral spine often more compressed than the aboral one, behind which are one or two very thick, blunt subadambulacral spines, and several bluntly pointed granules. Color in life orange to red-orange abactinally, actinal side pale yellow-cream.

Description. Large, broad, only slightly inflated, relatively rigid, R to 11 cm, R:r 1.7–1.8 ( Figs. 1–2 ); disc very broad, rays broad at base, sharply tapering; abactinal plates small, round or oval, each bearing a single short, blunt cylindrical or inflated (sometimes nearly spherical) spine, or rather short, wide, bivalve pedicellaria ( Fig. 3 ); plates edged with thorn-like granules. Madreporite small, irregularly ridged, located about half way between the anus and the edge of the disc. Marginal plates ( Fig. 4 ) in regularly paired rows; plates large, nearly round to quadrate, encircled by large (usually) pointed granules or thorns, and bearing one or two relatively large, thick, blunt, cylindrical or inflated (rotund) spines. Actinal plates larger than abactinal plates, and bearing large, thick tubercles, and some smaller, often thorn-like granules; plates adjacent to adambulacral plates ( Fig. 5 ) usually bear a single large, low, broad, bivalve pedicellaria. Adambulacral plates bearing two large, thick, blunt furrow spines, the aboral spine notably compressed, often only half as thick as the aboral spine; one or two large thick blunt subadambulacral spines and several smaller, thick, blunt, irregular tubercles. Oral plates ( Fig. 5 ) with three large, thick, blunt, strongly compressed marginal spines, 0–2 suboral spines, and seven to ten thick, blunt granules. Color in life ( Fig. 6 ) abactinal side bright orange, red-orange, or orange and red mottled; spine tips often paler; actinal side pale yellow-cream colored. Very rarely specimens may have some yellowish mottling abactinally.

Distribution. Aleutian Islands ( Fig. 7 ), SSW of Buldir Island (52° 16.53 N, 175º 58.73 E; NMFS 23-199701- 245) (leg. R. N. Clark, 9 August, 1997, trawled R/V Dominator, 141 m) to Krenitzin Islands, Unimak Pass, N of Tigalda Island (54° 22.83 N, 165° 04.05 W; NMFS 23-199901-14), at depths of 15– 250 m.

Habitat. Bedrock and boulders (at diving depths, <30 m), thickly encrusted with the coralline red algae Clathromorphum nereostratum . In deeper depths, the species occurs on bedrock, cobble, pebble, and sand/ gravel bottoms.

Etymology. Named for its distribution in the Aleutian Islands.

Remarks. Hippasteria aleutica sp. nov. superficially resembles H. phrygiana (Parelius, 1768) from the Atlantic-Arctic region in general form, but is distinguished by 1) the thorn-like granules surrounding the abactinal and marginal plates, those of H. phrygiana are smaller, and rounded; and 2) inferomarginals typically bearing two cylindrical or barrel-shaped spines, those of H. phrygiana usually bear several short thick, rounded knobs. The diagnostic characteristics of H. aleutica are consistent even in juveniles as small as R = 5 mm (LACM 1997- 154.013).

Hippasteria aleutica sp. nov. may be distinguished from Hippasteria spinosa Verrill, 1909 , Hippasteria armata Fisher, 1911 , and Hippasteria kurilensis Fisher, 1911 , by the thick, blunt, often inflated (barrel-shaped) spines, and the low, long bivalve pedicellaria of the abactinal surface. From Hippasteria heathi Fisher, 1905 , it is readily distinguished by 1) the lack of numerous short, stout, conical spines and tubercles on the actinal and marginal plates; 2) lack of large bivalve pedicellaria on marginal plates; and 3) color, which is uniformly white or cream in H. heathi . Hippasteria californica Fisher, 1905 , differs in 1) having oblong, oval to elliptical marginal plates; and 2) rugose or denticulate granules surrounding the abactinal and marginal plates, and occasional small pedicellaria.

Discussion. The pointed (often thorn-like) granules of the abactinal, and marginal plates shows affinity with Hippasteria kurilensis , and suggest a strong kinship with the Hippasteria spinosa species group. Additionally, although H. phrygiana is apparently wide spread and variable in the Atlantic Ocean (and adjacent Arctic Ocean), and may even penetrate into the extreme southern Pacific Ocean ( Mah, et. al., 2010). The isolation of H. aleutica sp. nov. in the extreme northern Pacific Ocean and absence of any Hippasteria spp. in Arctic North America ( Grainger, 1966, Bluhm, et. al. 2009) or Siberia (D’yakonov, 1950) suggests that a close (i.e. sub-specific) relationship with H. phrygiana is highly unlikely. Although there was no opportunity for a genetic analysis of Hippasteria spp. in this study, genetic samples have been taken from all nominal Alaskan species and are available for study.

The species of Hippasteria presently known from the Aleutian Islands are distributed as follows: Hippasteria spinosa is found in the SE Bering Sea, south to the vicinity of Unalaska Island, eastward into the Gulf of Alaska and southward to off California at depths of 20–600 m ( Fisher, 1911). In Aleutian waters H. spinosa occurs west to the vicinity of Unalaska Island. (R. N. Clark, pers. obs.). Hippasteria kurilensis is found throughout the Aleutian Islands (R. N. Clark, pers. obs.), and westward to the Kurile Islands ( Fisher, 1911; D’yakonov, 1950) at depths of 80– 600 m. Hippasteria heathi is found throughout the Aleutians Islands and Gulf of Alaska at depths of 250–500 m (R. N. Clark, pers. obs.). Hippasteria californica Fisher, 1905 occurs from southern California north to the Gulf of Alaska, north into the eastern Bering Sea (R. N. Clark, pers. obs.) and west across the Aleutian Is., to Hokkaido Island, Japan, at depths of 500–1820 m ( Mah, et. al. 2010). Hippasteria armata is found in the Kurile Islands ( Fisher, 1911; D’yakonov, 1950) Aleutian Islands (R. N. Clark, pers. obs.), Okhotsk Sea and western Bering Sea [D’yakonov, 1950 (as Hippasteria mammilifera D’yakonov, 1950 & Hippasteria colossa D’yakonov, 1950, respectively; fide R. N. Clark, based upon examination of type specimens), and the eastern Bering Sea at depths of 230– 650 m (R. N. Clark, pers. obs.).

Figures

FIGURE 7. Map of Aleutian Islands showing distribution of Hippasteria aleutica sp. nov.

FIGURES 1 – 6. Hippasteria aleutica sp. nov., Holotype, LACM 2008 - 030.001. Fig. 1, Whole animal, abactinal view. Bar = 5.0 cm. Fig. 2, Whole animal, actinal view. Bar = 5.0 cm. Fig. 3, Close-up, abactinal surface. Bar = 1.0 cm. Fig. 4, Close-up, marginal plates. Bar = 1.0 cm. Fig. 5, Close-up, adambulacral-oral region. Bar = 2.0 cm. Fig. 6, Live, in situ, Rat Island, 13 m (image R. N. Clark). R = 9.5 cm.