Stenohelia concinna Boschma 1964

Stenohelia robusta Boschma, 1964

Stenohelia profunda.—Marenzeller, 1904a:86, pl. 2: fig. 2; 1904b:91.

Stenohelia robusta Boschma, 1964a:69–72, fig. 2, pl. 1: figs. 7–9; 1968:437.—Vervoort and Zibrowius, 1981:28.—Cairns, 1983b:431.

DESCRIPTION.—Colonies small and uniplanar, the largest corallum (holotype) 2.7 cm tall and 2.7 cm broad, with a basal branch diameter of 4.3 mm. Seven to ten mm above corallum base, there is a spherical cavity caused by the symbiosis with a polynoid polychaete, much like the cavity found in Errina macrogastra. From this deformation radiate up to nine independent branches, usually diverging in a plane in the upper 180° of arc above the worm tube; however, sometimes branches diverge slightly out of the plane, producing a fuller colony. Branches robust, cylindrical, and straight; tapering gradually to branch tips. Branching axils greatly thickened and sometimes branching is trichotomous, giving a heavy or massive aspect to the colony. Coenosteum linear-imbricate in texture. Strips 80–90 μm wide, covered by broad but irregularly shaped platelets (Figure 12F,G). Coenosteum smooth, not ridged; however, numerous short papillae usually occur on coenosteum that forms worm tube.

Cyclosystems occur unilinearly on anterior face and also occasionally on posterior side on coenosteum that forms worm tube. Cyclosystems round, elliptical, and irregular in shape, e.g., 0.8 mm in diameter if round, 1.3 × 0.8 mm if elliptical. Greater axis of elliptical cyclosystems transverse to branch axis. Based on 60 cyclosystems, the range of dactylopores per cyclosystem is 12–19, average = 15.40 (σ = 1.92), and mode = 16.

Lower gastropore tube cylindrical and narrow, about 0.20 mm in diameter. Just above gastrostyle tip the tube greatly expands up to 0.50 mm in diameter (Figure 12B). Illustrated gastrostyle conical, 0.216 mm tall and 0.084 mm in basal diameter (H : W = 2.57). A gastrostyle figured by Boschma (1964a, fig. 2b) measured 0.35 mm tall and 0.15 mm in diameter (H : W = 2.33). Style pointed, the tip easily seen in an undamaged cyclosystem. Style unridged and covered with large pointed spines up to 35 μm long and 11 μm in diameter. Spines not arranged in rows. Dactylopore slits about 77 μm wide; dactylostyles rudimentary.

Female ampullae prominent hemispheres and round to elliptical in shape, e.g., 0.70 × 0.57 mm in diameter. Female ampullae smooth, with an efferent pore about 0.19 mm in diameter. Male ampullae also hemispherical and about same size (0.60–0.70 mm in diameter) but knobby, having one to six efferent pores, some of them raised up to 0.13 mm. Efferent pores about 32 μm in diameter. Both male and female ampullae occur sparingly on anterior faces of their respective colonies and shallow concavities appear in the coenosteum of both sexes following release of their gametes.

Nematocysts of dactylozooids 5.0–5.5 × 2.8–3.0 μm.

DISTRIBUTION.—Known only from the type-locality.

Stenohelia concinna Boschma, 1964

Stenohelia concinna Boschma, 1964a:69, 70, pl. 1: figs. 1–6; 1964b:74–77, fig. 1, pls 1, 2; 1968:437.—Vervoort and Zibrowius, 1981:28, 29.—Cairns, 1983b:431.

DESCRIPTION.—Colonies small and uniplanar, the largest corallum 2.6 cm tall and 1.6 cm broad; largest basal branch diameter 6.5 mm. Every colony has a spherical deformation caused by a polynoid polychaete, the worm tube being identical to that described for S. robusta and caused by same species of polychaete. Branches cylindrical and slender, the last two or three cyclosystems on a branch usually greater in diameter than branch supporting them. Coenosteal texture linear-imbricate. Coenosteal strips convex, 0.91–1.0 mm wide, and covered by broad, flat platelets. Coenosteal slits consistently 12–13 μm wide and bridged periodically by coenosteal extensions about 45 μm wide (Figure 14C, E). Low, broad papillae about 0.15 mm in diameter very common on basal branch and coenosteum overlying worm tube. Apical pores of papillae often elongate, e.g., 0.11 mm long and 0.015 mm wide.

Cyclosystems occur unilinearly on anterior face. Cyclosystems round, elliptical, and irregular in shape; an elliptical cyclosystem often 1.0 × 0.75 mm in diameter. Greater axis of elliptical cyclosystem transverse to branch axis. Based on 50 cyclosystems, the range of dactylopores per cyclosystem is 12–19, average = 15.54 (σ = 1.62), and mode = 15.

15.—Stenohelia concinna (A, B, female colony from ALB-3404): A, B, longitudinal section of cyclosystem revealing gastrostyle, × 66, × 180, respectively (B is a stereo pair).

Gastropore tube a narrow cylinder basally, about 0.25 mm in diameter, which flares into a spacious spherical cavity about 0.60 mm in diameter. The spherical cavity narrows to a cylindrical upper part about 0.45 mm in diameter (Figure 15A). Gastrostyle occupies lower third of gastropore chamber, filling lowermost cylinder and extending into spherical chamber. Gastrostyle conical and pointed, the illustrated style 0.35 mm tall and 0.16 mm in basal diameter (H : W = 2.2). A gastrostyle figured by Boschma (1964c, fig. 1b) measured 0.25 mm tall and 0.09 mm in diameter (H : W = 2.7). Gastrostyle covered by large, smooth, pointed spines up to 43 μm tall and 15 μm in basal diameter; spines not aligned. Dactylopore slits about 75 μm wide. Dactylostyles rudimentary: composed of one row of cylindrical elements about 24 μm tall and 10 μm in diameter.

Female ampullae hemispherical, 0.60–0.65 mm in diameter, and penetrated by numerous round coenosteal pores 25–35 μm in diameter. Efferent pore about 0.18 mm in diameter. Male ampullae roughly hemispherical, 0.55–0.60 mm in diameter, each with two or three apical efferent pores, each pore on a short conical mound about 50 μm tall; efferent pores about 27 μm in diameter. Male ampullae also extremely porous, penetrated by numerous large coenosteal pores. Both male and female ampullae clustered on all branch surfaces, especially on posterior face and around cyclosystems.

Gastro- and dactylozooid nematocysts not well preserved, but nematocysts 8–9 × 3–4 μm in size were found throughout the coenenchyme.

DISTRIBUTION.—Known only from the type-locality.

Crypthelia Milne-Edwards and Haime, 1849

DIAGNOSIS.—Gastro- and dactylopores arranged in cyclosystems, which occur exclusively on anterior branch faces. Cyclosystems covered partially or entirely by one or more fixed lids. Coenosteum linear-imbricate and often spinose as well. Nematopores common, especially on cyclosystem lids, pseudosepta, and ampullae. Gastropore double chambered; no gastro- or dactylostyles. Ampullae usually superficial and large, occurring in a variety of positions and with a variety of efferent pore locations. Female ampullae usually occur singly within cyclosystem lid and proximal cyclosystem wall; male ampullae usually clustered, often in compartmentalized rings around cyclosystems or in cyclosystem lid and proximal cyclosystem wall.

TYPE-SPECIES.—Crypthelia pudica Milne-Edwards and Haime, 1849, by monotypy.

calcareous colonies, no free medusae

166-806 m