Stylaster repandus Lindner & Cairns

Cairns, Stephen D. & Lindner, Alberto, 2011, A Revision of the Stylasteridae (Cnidaria, Hydrozoa, Filifera) from Alaska and Adjacent Waters, ZooKeys 158, pp. 1-88 : 35-36

Stylaster repandus Lindner & Cairns sp. n. Figs 27 A–C28A–M

Type material.

Holotype: 1 large dry male colony, and SEM stub 1504, USNM 1122740 (Fig. 27A-B). Paratypes: 52°21.20'N, 171°02.77'W, 475 m, 1 Sep 2000, 1 dry female colony, and SEM stub 1505, USNM 1122739; Amukta Pass, depth unknown, 1996, 2 dry male colonies, USNM 1122741. Type locality. 52°17.86'N, 170°58.28'W (southeast of Amukta Island), 375 m, 12 Sep 2000.

Etymology.

The specific name repandus (from the Latin, meaning "bent backwards", “undulate”) refers to the complexly folded coenosteal lamellae of this species.

Material examined.

Types.

Description.

Colonies firmly attached to a hard substrate by a robust basal stem and encrusting base, the base being 9 cm in diameter and the basal stem 5 cm in diameter in the case of the holotype. Immediately above basal stem the colony divides into two or three lamellae (Fig. 27C), each lamella (or sheet) of coenosteum increasing its surface area by folding its surfaces into a complex three-dimensional structure similar to that of Cyclohelia . Short (up to 15 mm) cylindrical branches project from plane of colony, but always in response to housing a parasitic spionid worm tube. Holotype (Fig. 27 A–B) 23 cm tall and 19 cm in width. Coenosteal lamellae thin at edge, only 2.0-2.5 mm thick, and thus easily damaged during collection; basal lamellae up to 10 mm in thickness. All colonies examined heavily infested with spionid worm tubes. Coenosteum reticulate-granular in texture, the strips being about 30 µm wide, bordered by slits about 9-19 µm thick; granules spinose. Coenosteum covered uniformly with small papillae (Fig. 28B). Coenosteum light orange, but central core a light shade of pink.

Cyclosystems equally common on both faces of lamellae, and even occur on lamellar edges, often arranged in transverse rows of up to 15 cyclosystems that parallel lamellar edge; diameter of cyclosystems 1.0-1.15 mm. Gastropore tube funnel-shaped near branch surface, and straight but constricted, the upper diameter being about 0.34 mm in diameter, the constriction corresponding to a diffuse ring palisade, the blunt elements being up to 60 µm tall and 40 µm in diameter. Gastrostyles lanceolate, pointed, and bear longitudinal, spinose ridges. Illustrated style (Fig. 28D) 0.53 mm in height and 0.26 mm in basal diameter.

Cyclosystems almost flush with coenosteum, the dactylopore slits raised only slightly above coenosteum; dactylotomes 0.15-0.17 mm in width. Based on 74 cyclosystems the range of dactylopores per cyclosystem is 1-11 (average = 3.94 (σ = 2.05), and mode = 4). In many cyclosystems there is an adcauline diastema (Fig. 28E), often produced by the infilling of 1-3 adcauline dactylopores, these dactylopores becoming obsolete. Dactylostyles robust, composed of an almost unilinear arrangement of cylindrical, blunt to clavate elements up to 60 µm tall and 13-15 µm in diameter (Fig. 28D, H, J–K).

Female ampullae (Fig. 28 L–M) low swellings on coenosteum 0.9-1.1 mm in diameter (internal diameter 0.7-0.8 mm), each with a peripheral efferent pore 0.3-0.4 mm in diameter that faces upward. Male ampullae (Fig. 28I) densely arranged, superficially visible only as inconspicuous mounds 0.5-0.6 mm in diameter (internal diameter 0.4-0.5 mm), often with an irregularly shaped apical efferent pore about 60 µm in diameter.

Remarks.

Among the 80 Recent species in the genus Stylaster ( Appeltans et al. 2011: www.marinespecies.org), Stylaster repandus is the only one to have a lamellate growth form. It is very similar in growth form to Cyclohelia lamellata and Errinopora undulata , and is one of five stylasterid species to have lamellate colonies (see Discussion of Errinopora undulata ).

Distribution.

Known only from three localities in the vicinity of Amukta Island, Aleutian Islands; 375-475 m.