Stylaster griseus, Cairns, Stephen D. & Zibrowius, Helmut, 2013

Cairns, Stephen D. & Zibrowius, Helmut, 2013, Stylasteridae (Cnidaria, Hydrozoa, Filifera) from South Africa, Zootaxa 3691 (1), pp. 1-57 : 28-30

Stylaster griseus sp. nov.

Figs. 2 C, 13A–M, 28

Etymology. Named griseus (Latin, meaning grey), for the colour of the coenosteum.

Types and Type Locality. Holotype: PF 13063, colony of indeterminate gender, SAM H1459. Paratypes: MN SM163, 3 poor fragments, SAM; MN SM179, 1 female colony (in alcohol), SAM, and SEM stub 1701 (USNM); MN SM180, 1 colony base, SAM; MN SM184, 22 worn fragments, SAM; MN SM185, 1 male and 3 indet. colonies (in alcohol), SAM, and SEM stub 1715 (USNM); PF 808, 1 colony, indet., SAM H1231; PF 907, 1 male and 3 indet. colonies, SAM H1467; PF 13654, 2 female and 1 male colonies, SAM H1460, and SEM stub 1699–1700 (USNM); UCTES SCD289, 1 female colony, RMNH 15820; UCTES SCD296, 1 male colony, RMNH 15826. Type Locality: off Hood Point Lighthouse (Eastern Cape Province), South Africa, 90 m.

Material Examined. Types.

Description. Colonies are of moderate size, robust, uniplanar, and sparsely branched, the largest colony (the holotype, Fig. 2 C) 7 cm tall and 6 cm wide, with a basal branch diameter of 14.1 mm. Branching is dichotomous but not regular, the blunt, cylindrical branch tips 2–4 mm in diameter. There are no polynoid commensals. The coenosteal texture is a fine reticulate-granular, the strips ranging from 53–72 µm in width, each covered with small, irregularly-shaped granules ( Fig. 13 D, F). Nematopores were not observed. The colonies are light grey to light brown in colour, and chalky white when dead.

Cyclosystems ( Fig. 13 B) are uniformly arranged on all branch surfaces, although sometimes arranged in longitudinal rows up to 15 cyclosystems in length. Cyclosystems are slightly raised above the coenosteum and circular in shape, 0.9–1.13 mm in diameter. Based on 50 cyclosystems, the range of dactylopores per cyclosystem is 7–12; the average is 9.22 (ơ = 1.30); and the mode is 9. Diastemas occur occasionally but are rarely wider than two pseudosepta.

The gastropore is circular (about 0.43 mm in diameter), and the deep gastropore tube is cylindrical, as much as 1.4 mm in depth. The base of the gastrostyle is a short cylinder about 0.35 mm in diameter, which supports a discoidal torus that is 0.40–0.50 mm in diameter. Above the torus is a tall slender apical spine, the entire gastrostyle measuring up to 0.64 mm in height ( Figs. 13 F, G). At the level of the base of the apical spine the gastropore tube constricts as a sphincter (a continuous in structure like a low belt about 68 µm in width and 36 µm in height, not composed of discrete cylindrical elements, Figs. 13 F, G). The dactylotomes are 0.09–0.13 mm in width, and the pseudosepta are 0.07–0.25 in width, their upper surfaces convex ( Fig. 13 C). Each dactylopore contains 1–3 dactyloglossae, usually getting larger with greater depth in the pore. The dactyloglossae are semi-circular (or broadly tongue-shaped), about 0.08–0.10 mm wide and 0.09 mm in height, and about 20 µm thick, although their outer margins appear to be the thickest ( Figs. 13 H–L). The larger uppermost dactyloglossae occlude about onethird of the dactylopore.

Female ampullae are primarily internal, hardly seen in surface view, and are about 0.9 mm in internal diameter, opening via an efferent pore into the upper chamber of an adjacent gastropore tube. Male ampullae are also primarily internal, but can be seen in apical view as small (0.35–0.40 mm in diameter) mounds, each with a small apical efferent pore ( Figs. 13 A, M).

Comparisons. Stylaster griseus is quite similar to S. bithalamus in many characters, and, after examination of more specimens, may prove to be a subspecies or just a distinctive form of the latter. The species are similar in coenosteal texture, in lacking nematopores, their female and male ampullar shapes, gastrostyle shape, and presence of dactyloglossae, as well as overlapping in distribution and depth range. S. griseus , however, seems to consistently differ ( Table 1 ) in having, a gray to light brown corallum, blunt branch tips, a slightly higher average and modal number of dactylopores per cyclosystem, and in lacking polynoid gall tubes.

Distribution. Known only from off the continental shelf off the Eastern Cape Province (Fig. 28), 80– 155 m.

Figures

FIGURE 2. Colonies of various species: A – B, Stylaster bithalamus, MN SM 185, male, anterior and posterior views of same colony, respectively. C, Stylaster griseus, holotype. D – F, Stylaster amphiheloides, syntypes, BM 1842.12.2.79. G – H, Stylaster amphiheloides, MN SM 228, posterior and anterior views of same colony. I, Stylaster lonchitis, Liltved specimen. J, Stylaster kenti, holotype.

FIGURE 13. Stylaster griseus (A, C, F, H, J, L – M, male paratype colony from PF 13654, SAM H 1460; B, D – E, G, K, indet. gender from PF 13654, SAM H 1460; I, female from MN SM 179, SAM): A, stereo view of cyclosystems and male ampulla. B, a cyclosystem with a narrow diastema. C, several pseudosepta. D – E, reticulate-granular coenosteal texture. F, stereo view of gastrostyle and sphincter. G, gastrostyle. H – L, cross-section of dactylopore tubes showing various sizes of dactyloglossae. M, male ampullae.