Stylaster elassotomus Fisher, 1938

Cairns, Stephen D. & Lindner, Alberto, 2011, A Revision of the Stylasteridae (Cnidaria, Hydrozoa, Filifera) from Alaska and Adjacent Waters, ZooKeys 158, pp. 1-88 : 50-52

Stylaster elassotomus Fisher, 1938 Figs 21C25 A–G

Stylaster elassotomus Fisher, 1938: 499-500, pl. 41, fig. 3, pl. 42, figs 1-1c, pl. 49, fig. 1.- Boschma 1957: 7.- Wing and Barnard 2004: 11 (key), 28.- Heifetz et al. 2005: 134, 137 (listed).- Stone and Shotwell 2007: 108 (listed).-Jameison et al. 2007: 224 (listed).

Type material.

Holotype: 1 dry male colony, and SEM stub 1507, USNM 43268 (Fig. 21C). The pale pink paratype 5 cm in length (USNM 86007) mentioned by Fisher is an unidentified Stylaster having little in common with the holotype. Type locality.Albatross 4781, 52°14'30"N, 174°13'E (off Agattu Island), 882 m.

Material examined.

Types.

Description. Holotype (Fig. 21C) colony bushy, 5.5 cm tall and 4.5 cm wide, attached by a basal branch 6 mm in diameter. Branches do not anastomose and are circular in cross section. Coenosteum reticular-granular in texture, the strips 55-60 µm in width, separated by slits 10-14 µm wide; strips covered with small angular granules. Spionid worm tubes absent. Coenosteum white.

Cyclosystems circular to slightly elliptical, 1.0-1.2 mm in diameter, arranged exclusively on branch edges in an alternating fashion, most projecting perpendicular to branch. Gastropores circular and quite large (0.5-0.6 mm in diameter), occupying up to 55% of cyclosystem diameter (Fig. 25F). Gastropore tube cylindrical, curved, and long, such that gastrostyle tip is rarely seen when viewed from above (Fig. 25A). A delicate ring palisade (Fig. 25 C–D) occurs near gastrostyle tip, composed of slender cylindrical elements up to 60 µm long and 25 µm in diameter. Gastrostyle slender (H:D = 4.4), the illustrated style 0.53 mm in height, occupying lower quarter of gastropore tube (Fig. 25A).

Dactylotomes 60-80 µm wide but very short as well as having short internal slits, thus contributing to the large size of the gastropore tube (Fig. 25F); dactylostyles inconspicuous. Range of dactylopores per cyclosystem 11-17 (n = 21, average = 14.40 (σ = 1.36), and mode = 15). Supernumerary dactylopores common (Fig. 25B), 70-100 µm in diameter. Pseudosepta same width as dactylotomes; diastemas rare.

Female ampullae unknown. Male ampullae (Fig. 25G) hemispherical, 0.5-0.6 mm in diameter.

Remarks.

Despite access to a diverse stylasterid collection from the Aleutian Islands, no unequivocal additional specimens could be identified as Stylaster elassotomus , even the paratype of the species not considered to be conspecific. Its distinctive characteristics of having a highly curved gastropore tube, slender ring palisade elements, and a very large gastropore surrounded by very short dactylotomes and pseudosepta distinguish it from all other Alaskan species (see Table 2).

Distribution.

Known only from type locality.