Clarkiella discoveryi Heding, in Heding & Panning, 1954

(Figures 11 – 12)

Clarkiella discoveryi Heding, in Heding & Panning, 1954: 119 – 120, pl.49. Material examined. Holotype: 1 Mil W. off. Shag Rocks, South Georgia, 199 m, 19.xi. 1930, 60 mm length (ZMUC – HOL 64). Paratype: same data as holotype, 45 mm length (ZMUC – HOL 247). Holotype Slides MNHN – IE –2005–6324); (MNHN – IE –2005–6325); (MNHN – IE –2005–6326)

Redescription. Body U–shaped; tube feet scattered throughout body (Fig. 11a). Color, in ethanol, beige. 15 dendritic tentacles, two ventral smaller (Fig. 11b, c). Anal papillae present (Fig. 11d). Longitudinal, retractor and circular muscles thin (Fig. 11e, f). Longitudinal muscles split posteriorly (Fig. 11f). Retractor muscles short, attached to middle of radial plate (Fig. 11h). Stone canal single, short, ending in elongated madreporite (Fig. 11g). Radial and interradial plates of calcareous ring of same height, laterally connected to each other for most of their length (Fig. 11h, i). MidIR (IR5) taller than other, lacking posterior projection (Fig. 10i); midR (RI) not modified. Radial plates undivided, rectangular, convex base with posterior projection and 2 AP, one wider than the other (Fig. 10h). Interradial plates undivided, elongated, with two posterior projections and pointed anterior end (Fig. 10 h, i). radial and interradial plates lacking posterior processes.

Body wall with two–pillared tables with circular disc (80–100 μm long; Fig.12 a, b); disc with four central holes and 8–10 marginal perforations, margin undulated; spire ending in about 12 spines. Tentacles with perforated plates (100–150 μm long; Fig.12c, d). Introvert with closed rosettes (70–110 μm long; Fig. 12e, f). Tube feet with endplate with small holes, larger ones around margin, smaller ones medially, endplates up to 150 μm in diameter and tables like body wall.

Remarks. Here we provide a photograph of the general aspect of the holotype (Fig. 11a) and describe by means optical microscopy for the first time the morphology of its longitudinal retractor and circular muscles (Fig. 11e, f).