Stylaster kenti, 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 : 34-35

Stylaster kenti sp. nov.

Figs. 2 J, 16A–G, 22

Etymology. Named in honor of W. Saville Kent, in recognition of his description of the first stylasterids from the South African coast (Kent 1871).

Types and Type Locality. Holotype: MN SM43, 1 male colony, SAM, and SEM stubs 1706–07 (USNM). Paratypes: MN SM43, 1 male branch fragment and 3 female branch fragments, SAM, and SEM stub 1708 (USNM). Type Locality: 28°45.5’S, 32°24.5’W (off Richards Bay, Natal), 360– 420 m.

Material Examined. Types.

Description. Colonies are relatively small and uniplanar in shape, the largest colony (the holotype, Fig. 2 J) measuring 4.1 cm in height and 3.1 cm in width, having a broken basal branch diameter of 5.0 mm. Branching is dichotomous. The coenosteal texture is reticulate-granular ( Fig. 16 C), the strips ranging from 50–70 µm in width, and are covered with low rounded granules. Nematopores and commensal worms are not present. The corallum is light brown, fading to off-white near the branch tips.

The cyclosystems are closely spaced and arranged linearly on all branch edges, alternating in a sympodial manner ( Fig. 2 J). Cyclosytems are elliptical to elongate in shape, the greater axis being up to 1.4 mm in length ( Fig. 16 B). Based on 50 cyclosystems, the range of dactylopores per cyclosystem is 8–15; the average is 12.42 (ơ = 1.25); and the mode is 13. Diastemas are not present.

The gastropores are circular (0.30–0.40 mm in diameter), and the gastropore tube is long (up to 1.6 mm) and cylindrical, about three times the length of the gastrostyle, widening into a spherical gastropore chamber proximally. The gastrostyle has a short cylindrical base, which supports a toroidal middle section, topped by a vertical spine, the entire style being about 0.5 mm in height, the distal spine constituting about 60% of that height. The middle and upper portions are covered with spines, those on the distal spines being much coarser ( Fig. 16 F). At the level of the upper gastrostyle spine the tube is constricted by a belt-like sphincter ( Fig. 16 F), which is about 90 µm in width. The pseudosepta range from 0.10–0.22 mm in maximum width, whereas the dactylotomes are 0.90– 0.10 in width. Each dactylopore contains several linearly arranged dactyloglossae ( Figs. 16 D, E) that serve as baffles that occlude most of the dactylopore tube.

Female ampullae are low swellings about 1.2 mm in diameter that always occur near cyclosystems ( Fig. 16 B). Their efferent pores open into the upper gastropore tube. Male ampullae are considerably smaller (0.3–0.5 mm in diameter), irregular in shape, and occur in clustered on all branch surfaces ( Figs. 16 A, G). They have small apical efferent pores. Both types of ampullae often have a single small (0.09–0.10 mm diameter) round pore that appear to have been drilled through their surface, perhaps by a gastropod predator as noted in the genus Adelopora (see Cairns 1982).

Comparisons. As mentioned in the Material and Methods section, only six stylasterid species are known to have dactyloglossae, and only one other than S. kenti belonging to Stylaster (Group C): S. amphiheloides . Although similar, S. kenti differs from that species in lacking commensal polynoid gall tubes, having a brown corallum, and having irregularly-shaped (not conical) male ampullae. And, although somewhat similar in colour, gastrostyle morphology, and dactyloglossae, S. kenti differs from S. griseus in cyclosystem placement, number of dactylopores per cyclosystem, and depth range.

Stylaster kenti is also similar S. brunneus Boschma, 1970 in coenosteal colour and colony shape, but differs in almost every other character, including placement of cyclosystems, dactylostyle morphology, coenosteal texture, and female ampullae size and efferent pore location. Furthermore, S. brunneus is known only from the New Zealand /New Caledonian region (Cairns 1991).

Distribution. Known only from the type locality (Fig. 22).

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 16. Stylaster kenti (A, C, F – G, male holotype, MN SM 43, SAM; B, D – E, female paratype from MN SM 43, SAM): A, stereo view of a cyclosystem and several male ampullae. B, stereo view of a cyclosystem. C, reticulate-granular coenosteal texture. D – E, various dactyloglossae (E a stereo pair). F, stereo view of a gastrostyle and sphincter. G, male ampullae.