Stylaster amphiheloides Kent, 1871

Cairns, Stephen D. & Zibrowius, Helmut, 2013, Stylasteridae (Cnidaria, Hydrozoa, Filifera) from South Africa, Zootaxa 3691 (1), pp. 1-57 : 30-32

Stylaster amphiheloides Kent, 1871

Figs. 2 D–F, 14A–L, 29

Stylaster amphiheloides Kent, 1871: 277 –278, pl. 24, figs. 1a–c.—not Hickson & England, 1905: 13.—Boschma, 1957: 2; 1966b: 112.

Stylaster ampheliodes: Cairns, 1983b: 430 (listed, misspelled).

Types and Type Locality. The primary syntypes are deposited at the BM (1842.12.2.74–80). Three syntype fragments are also at the Naturalis Biodiversity Centre (RMNH 15319) and a fragment and SEM stub 1709 at the NMNH (USNM 85785). Type Locality: Cape of Good Hope, depth not recorded.

Material Examined. Galathea 196, fragments, ZMC; Galathea 197, 1 colony, ZMC; MN SM38, 38 colonies, SAM; MN SM85, 3 colonies, SAM; MN SM86, 2 colonies, SAM; MN SM90, 3 colonies, SAM; MN SM92, 1 colony, SAM; MN SM94, 5 colonies, SAM; MN SM103, 7 colonies, SAM; MN SM107, 27 colonies, SAM; MN SM123, 2 colonies, SAM; MN SM129, 5 colonies, SAM; MN SM131, 4 colonies, SAM; MN SM162, 30+ fragments, SAM; MN SM165, 30+ fragments, SAM; MN SM226, 5 colonies (including 3 in alcohol), SAM; MN SM228, 27 colonies (including 18 in alcohol), SAM, and SEM stub 1713 (USNM); MN SM232, 14 colonies (2 in alcohol), SAM; MN SM234, 2 colonies, SAM; MN SM237, 2 colonies (1 in alcohol), SAM; PF 907, 2 colonies, SAM H2816; PF 1915, 4 colonies, SAM H1463; PF 2819A, 10 colonies, SAM H1462, and SEM stub 1711–12 (USNM); PF 12729, 1 colony, SAM H1457, and SEM stub 1710 (USNM); PF 14743, 1 colony, SAM H1504; PF 17995, 1 colony, SAM H1464; syntypes from BM, NMNH and Naturalis Biodiversity Centre. Reference Material: specimens reported by Hickson & England (1905).

Description. Colonies are relatively small, rarely exceeding 3.5 cm in height, but may be equally or as wide as their height; colonies are uniplanar or bushy. Branching is dichotomous, the distal branches quite delicate, terminating in a terminal cyclosystem. Commensal polynoid tubes present in all colonies, starting at a very small colony size, the tubes being rectangular in cross section, about 5 x 2.5 mm in cross section ( Figs. 2 E, F). The tube is interpreted as occurring on the posterior side of the colony. The coenosteal texture is reticulate granular ( Figs. 14 B, C), the strips 75–120 µm in width, and covered with low rounded granules. In some colonies the coenosteum is flat, almost porcellaneous, the granules covered by smooth coenosteal deposits. The colonies are uniformly white.

Cyclosystems are arranged exclusively on the branch edges, characteristic of Group C species, and only in rare cases having some cyclosystems on the anterior face. Delicate distal branches have cyclosystems arranged in a regular sympodial manner. Cyclosystems are circular to slightly irregular in shape ( Fig. 14 A), and 1.3–2.0 mm in greater diameter. Based on 50 cyclosystems, the range of dactylopores per cyclosystem is 9–21; the average is 13.9 (ơ = 2.46); and the mode is 13. Diastemas are rarely present, but only in cyclosystems on the main branch.

The gastropores are circular (about 0.6 mm in diameter), and the gastropore tube is straight and cylindrical. The gastrostyle has a short cylindrical base, a toroidal mid-section, and a tall slender apical spine, which projects through a belted sphincter ( Figs. 14 G–I). The gastrostyles range from 0.5 to 0.8 mm in height, occupy 1/3 to ½ of the gastropore tube, and have a L:D ratio of 1.1–2.6, those parameters depending on the length of the apical spine. The dactylotomes are 0.10–0.12 mm in width, and the pseudosepta are 0.15–0.16 mm in width, with convex upper faces. Each dactylopores contains a series of dactyloglossae ( Figs. 14 D–F), each up to 0.11 mm in width, which occlude most of the dactylopore tube.

Female ampullae are visible externally as low swellings 1.1–1.2 mm in diameter that are invariable located in clusters around a cyclosystem; their efferent pores open into the adjacent upper gastropore tube ( Fig. 14 J) through a pore 0.17–0.22 mm in diameter. Male ampullae are scattered over the coenosteum and occur even on the polynoid gall tube. They are shaped as small cones, up to 0.35 mm in height, 0.15 mm in distal diameter, and 0.4–0.6 mm in basal diameter, giving these colonies a spiny appearance ( Figs. 14 K, L). Each bears 1–3 tiny (25 µm diameter), irregularly-shaped efferent pores.

Comparisons. Even though they are placed in different species groups, S. amphiheloides and S. bithalamus are quite similar. S. amphiheloides can be distinguished by having its cyclosystems relegated only to its branch edges, having a higher number of dactylopores per cyclosystem (average 13.98 vs 11.0), and in having conical male ampullae. Furthermore, S. amphiheloides is thus far known only from 155–1000 m, whereas S. bithalamus appears to be a shallower water species at 11– 155 m.

Remarks. As Boschma (1966b) suggested, the deeper-water records reported by Hickson & England (1905) from Indonesia are not S. amphiheloides , those specimens similar only in having a commensal polynoid worm.

Distribution. From Cape Town to Richards Bay ( Natal)(Fig. 29), 155–1000 m, although most records deeper than 500 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 14. Stylaster amphiheloides (A, male syntype, USNM 85785; B, E – F, H – J, female from PF 2819 A, SAM H 1462; male from K – L, MN SM 328, SAM): A, stereo view of a cyclosystem. B – C, reticulate-granular coenosteal texture. D, stereo view of a damaged cyclosystem showing some dactyloglossae. E – F, dactyloglossae. G, stereo view of a gastrostyle from above. H, stereo view of a gastrostyle and sphincter. I, elongate gastrostyle and sphincter. J, longitudinal fracture of gastropore tube showing a female efferent pore. K – L, male ampullae.