Stylaster crassiseptum 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 : 52-54

Stylaster crassiseptum Lindner & Cairns sp. n. Figs 21D26 A–J

Type material.

Holotype: dry female branch fragment 12 cm in length, plus many smaller broken pieces, and SEM stubs 1520-1521, 1546, USNM 1122531 (Fig. 21D). Paratypes: North Pacific, 52°04'17"N, 176°59'21"E, 366 m, date unknown, 1 female, USNM 1122511; Shishaldin, 54°00'41"N, 179°46'52"E, 291 m, 14 Mar 2000, 1 female, USNM 1122497; Shishaldin, 53°56'24"N, 179°49'31"E, 318 m, 14 Mar 2000, 1 male, and SEM stub 1522-23, USNM 1122519; Shishaldin, 51°48.49'N, 174°29.92'W, 531m, 2000, 1 female, USNM 112527. Type locality.Shishaldin station, 53°59'50"N, 179°46'52"E (off Bowers Bank, Aleutian Islands), 291 m, 5 Mar 2000.

Etymology.

The specific name crassiseptum (from the Latin crassus, meaning "thick" + septum meaning "wall"), in reference to the wide pseudosepta of the cyclosystems.

Material examined.

Types.

Description.

Colonies primarily uniplanar, having no branch anastomosis. Holotype (Fig. 21D) a branch fragment 12 cm in length and 1 cm in basal branch diameter; largest specimen (USNM 1122527) an intact colony 24 cm in height and 19 cm wide, with a basal branch diameter of 4.5 cm. Distal branches circular in cross section, basal branches somewhat rectangular in cross section, the longer axis perpendicular to colony plane; symbiotic polychaetes absent. Coenosteum reticulate-granular in texture, coenosteal strips 60-70 µm in width, separated by very narrow slits only 3-5 µm wide; coenosteal strips not linearly arranged near cyclosystems. Coenosteal granules very low and smooth, conferring a shiny or porcellaneous texture to branches. Coenosteum dense and uniformly pale orange.

Cyclosystems circular, slightly exsert, and relatively small (0.7-1.0 mm in diameter), occurring exclusively on branch edges (Fig. 26A) in alternating fashion (Fig. 26B), most projecting perpendicular to branch. Cyclosystems well spaced, separated by 1-3 cyclosystem diameters from one another on one side of a branch. Gastropores circular, about 0.5 mm in diameter; gastropore tubes cylindrical and slightly curved, having a well-developed ring palisade (Fig. 26I) composed of numerous large squat elements up to 35 µm in height and 50 µm in diameter. Gastrostyles lanceolate and slender, the figured style being 0.48 mm in height and only 0.15 mm in diameter (Fig. 26I), the tip usually seen when viewed from above. Gastrostyle covered with blunt spines up to 33 µm in length.

Dactylotomes slender and uniform in width (60-70 µm); dactylostyles quite robust (Fig. 26G), the large cylindrical elements (up to 45um tall and 13 µm in diameter) almost completely filling the lower dactylopore, but because of the narrow dactylopores and exsert pseudosepta, the dactylostyles are barely visible in an intact cyclosystem. Range of dactylopores per cyclosystem 6-12 (n=60, average = 8.89 (σ = 1.4), mode = 9). Supernumerary dactylopores not present. Pseudosepta solid, exsert, and variable in width (0.15-0.31 mm in width), or up to five times width of adjacent dactylotomes (Fig. 26 C–E). Diastemas rare.

Female ampullae (Fig. 26J) smooth superficial hemispheres 0.9-1.1 mm in diameter, with a lateral efferent pore about 0.3 mm in diameter. Male ampullae (Fig. 26A, H) often clustered, slightly irregular in shape, 0.45-0.50 mm in diameter, often with one or more tiny (28-30 µm in diameter) apical efferent pores.

Remarks.

Although similar to Stylaster alaskanus , Stylaster crassiseptum is distinguished by having non-anastomosing branches, a curved gastropore tube, relatively wide pseudosepta, and more robust dactylostyles (Table 2).

Distribution.

Aleutian Islands from off Kiska to off Atka Islands, Bowers Bank; 291-531 m.