Stylaster trachystomus (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: 42-43

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Stylaster trachystomus (Fisher, 1938)

new rank

Stylaster trachystomus (Fisher, 1938)   new rank Figs 17H20 A–M

Allopora campyleca trachystoma   Fisher, 1938: 510-511, pl. 45, fig. 2, pl. 46, pl. 54, figs 1-1b.-? Naumov 1960: 579.- Lowenstam 1964: 382 (mineralogy).

Stylaster campylecus trachystomus   .- Cairns 1983b: 430.- Cairns and Macintrye 1992: 100-101 (mineralogy).- Wing and Barnard 2004: 27.- Heifetz et al. 2005: 134 (listed).- Stone and Shotwell 2007: 108 (listed).-Jameison et al. 2007: 224 (listed).

Type material.

Holotype: Alb-4784, 1 dry female colony 9 cm in height, and SEM stubs 1516, 1541, USNM 43265 (Fig. 17H). Paratypes: Alb-4784, 2 female, 2 male, 1 indet. colonies, and SEM stub 1517-18, dry, USNM 76811. Type locality.Alb-4784: 52°55'40"N, 173°26'E (off East Cape, Attu Island, Aleutians), 247 m.

Material examined.

Types; Delta 5999-8E-3, 51°21.042'N, 179°30.483'W, 115 m, 4 Jul 2003, 1 male, AB10-0001; Delta 6230 –20– 18, 52°28.142'N, 173°35.882'W, 190 m, 8 Jul 2004, 5 male branch fragments in alcohol, AB10-0004; Shishaldin, 54°54.09'N, 178°37.27'E, 366 m, 11 Feb 2000, 1 female, 2 male, AB00-45.


Corallum uniplanar, occasionally with short side branches oriented perpendicular to flabellum; branch anastomosis occurs only in large-diameter basal branches. Largest colony (paratype) 12 cm tall and 8 cm wide, with a basal branch diameter of 3 × 1.5 cm. Distal branches circular to slightly flattened in cross section. Commensal spionid worm tubes common. Coenosteum reticulate-granular in texture, the coenosteal strips 70-80 µm wide, the slits discontinuous and about 10-15 µm wide, the small granules producing a rough texture. On exsert cyclosystems, coenosteal strips are parallel and straight. Most coralla bear some short coenosteal ridges, called "spinous outgrowths" by Fisher (1938: 511), these thin ridges aligned with the branch (up to 1 mm long, 1 mm tall, and only 0.1 mm in width) or aligned with some of the pseudosepta on exterior wall of a cyclosystem (Fig. 20 G–H). Coenosteum pale pink-orange.

Cyclosystems arranged uniformly on branches, not linearly, but fewer in number on posterior face. Cyclosystems rarely circular in shape, rather elliptical or asymmetrical, the longer axis of the ellipse up to 1.8 mm. Gastropore tubes cylindrical, slightly curved, and quite deep (up to 3 mm); a well-developed ring palisade present near gastrostyle tip, composed of squat elements about 50 µm in height and width. Gastrostyles lanceolate, up to 0.67 mm, having a H:D of about 3.1, and occupying lower quarter of gastropore tube. Because of curvature of the long gastropore tube, the short gastrostyle, and the wide pseudosepta, the gastrostyle tip is rarely seen when viewed from above.

Dactylotomes 0.085-0.10 mm in width, supernumerary dactylopores being quite rare, usually associated with pseudosepta. Dactylostyle inconspicuous (Fig. 20J). Range of dactylopores per cyclosystem 8-18 (n = 50, average = 11.82 (σ = 2.15), and mode = 11). Pseudosepta slender (0.07-0.21 mm wide), adcauline diastemas twice that width sometimes present; surface of pseudosepta quite porous (Fig. 20F).

Female ampullae (Fig. 20D, G, K–L) superficial hemispheres 1.0-1.3 mm in diameter, having a knobby or papillose surface; efferent pores not evident in material at hand. Male ampullae (Fig. 20M) also superficial swellings 0.50-0.55 mm in diameter. Both types of ampullae clustered on anterior and posterior branch faces.


Fisher (1938) described this taxon as a subspecies of Stylaster campylecus   , distinguishing it from the nominate subspecies by having spongy pseudosepta (Fig. 20F), decurrent pseudoseptal ridges on the inside of the gastropore tube (Fig. 20C), and spiny coenosteal outgrowths (Fig. 20 G–H). Stylaster trachystomus   is otherwise similar to typical Stylaster campylecus   in gastropore tube and gastrostyle shape and number of dactylopores per cyclosystem, but is also similar to Stylaster brochi   in arrangement of cyclosystems and in hosting commensal spionid polychaetes; it also has unique characteristics as mentioned above (see also Table 2). Although few colonies are known of this species, because it does present a unique set of characteristics, it is considered valid and herein elevated to species rank. The corallum was found to be 100% aragonitic according to Cairns and Macintrye (1992).


Aleutian Islands: from off Attu Island and north of Amalia Island (Andreanof Islands), including Bowers Bank; 115-366 m.