Stenohelia spinifera sp. nov.

Figs. 3 B, 18A–M, 31

Etymology. From the Latin spiniferus, meaning spine bearing, an allusion to the prominent and densely packed nematopore tubes.

Types and Type Locality. Holotype: PF 13479, 1 male colony, SAM H1461, and SEM stub 1692 (USNM). Type Locality: off Sandy Point (near Cape Morgan, northern Eastern Cape Province), 174 m.

Material Examined. Type.

Description. The holotype (Fig. 3 B) is uniplanar, 2.8 cm tall and 1.95 cm wide, with a basal branch diameter of 3.8 mm. Branch anastomosis does not occur. The coenosteum is composed of reticulate strips 40–60 µm in width, each strip covered with bundles of slender rods, the rods 9–10 µm in length and about 2 µm in diameter, producing a rough microtexture (Fig. 18 E, F). The coenosteum, as well as the sides of the cyclosystems and ampullae, are densely covered with tall (up to 0.26 mm), slender papillae (nematopore tubes, Figs. 18 A–C, G, H), each with an apical pore 19–27 µm in diameter, sometimes 2 or 3 papillae fusing into a wider ridge having 2 or 3 apical pores. Altogether these nematopores spines produce a characteristically spiny aspect. The coenosteum is white.

Cyclosystems are unifacial in placement, positioned in a staggered arrangement on the anterior branch face (Fig. 3 B). Cyclosystems are circular to slightly elliptical in shape, with a somewhat sinuous outer edge due to the high concavity of the pseudosepta; cyclosystems are up to 1.6 mm in greater diameter. The holotype bears 45 cyclosystems. Based on 26 cyclosystems, the range of dactylopores per cyclosystem is 12–15; the average is 13.35 (ơ = 0.098); and the mode is 14.

Gastropores are round and about 0.40 mm in diameter; the gastropore tube is elongate and curved 90°, characteristic of the genus, such that the tip of the gastrostyle is not visible. The gastrostyle occupies the lower spherical portion of the gastropore tube, which is about 70 µm in diameter. It is supported by a short. cylindrical (about 0.3 mm in diameter) pedestal that supports a toroidal middle section about 0.55 mm in diameter and 0.2 mm tall (Fig. 18 K, L). Above this section is an apical spine of unknown dimensions (Fig. 18 K); there is no ring palisade or sphincter. The middle and upper portions are densely covered with laterally fused spines, the spines up to 0.13 mm in length (Fig. 18 M). The dactylotomes are consistently 0.09–0.10 mm in width, whereas the pseudosepta (measured at their outer edge) are wider and somewhat more variable in width, ranging from 0.15–0.24 mm in width. The upper faces of the pseudosepta are highly concave. Each dactylopore contains at least one dactyloglossa, roughly level with the coenosteal surface, seen best in damaged cyclosystems (Fig. 18 I). The dactyloglossae are roughly circular in shape, about 0.11 mm in diameter, and block about 80% of the dactylopore tube.

Male ampullae are superficial, irregularly-shaped mounds 0.6–0.7 mm in diameter (Figs. 18 J, L), and occur primarily on the anterior branch surface; each has an apical efferent pore about 60 µm in diameter. Each male ampulla is covered with 5–10 tall nematopores spines, making them look quite spiny. Female ampullae are unknown.

Comparisons. Although two other species ( S. umbonata (Hickson & England, 1905) and S. echinata Eguchi, 1968) have coenosteal papillae (either nematopore tubes or ridges), S. spinifera differs in having dense, uniformly arranged papillae. It is also distinctive in having dactyloglossae, a character shared with only one other species in the genus, S. venusta .

Remarks. Stenohelia spinifera was collected at the precise locality and depth as S. venusta but ten days later. Although they are the only two species in the genus to have dactyloglossae, S. spinifera can be distinguished by bearing large coenosteal papillae, having a rough coenosteal texture, having on average less dactylopores per cyclosystem, and in having irregularly shaped male ampullae primarily on the anterior branch faces.

Distribution. Known only from one record, the type locality (Fig. 31).