Ekkentropelma groovia Thandar, 2006, sp. nov.

Ekkentropelma groovia sp. nov.

Figure 14

Diagnosis

Small U­shaped species, mature holotype 8.75 mm along ventral surface, oral or anal cones absent. Colour in alcohol yellowish­white. Sole distinct, enclosed within groove that is displaced slightly to right, extending from just behind the mouth to terminate just in front of anus. Dorsal podia few, apparently restricted to ambulacra and emitting from between scales. Podia of sole larger, fewer, 3–5 on each side. Anal teeth minute. Tentacles about 10, finger­shaped, with minute lateral branches. Dorsal body wall encased in simple, smooth or slightly knobbed, one­layered, imbricating scales, up to 380 µm long, and much smaller, up to 220 µm long, smooth or slightly knobbed plates with up to 10 holes and often with one end slightly prolonged; baskets absent.

Type

SAM A­ 27913.

Type locality

Between Port St. Johns and East London, 32 28.6’ S, 28 58.8’ E, R.V. ‘Meiring Naude’, St. SM 226, 24.vi.1979, 710– 775 m.

Material examined

Holotype (female).

Etymology

The specific name is with reference to the groove in which the sole is embedded.

Description

Specimen (Figure 14 I) small, somewhat U­shaped, cylindrical, without oral and anal cones, mouth and anus terminal. Mouth not bordered by valves; tentacles retracted; anus terminal but downwardly directed. Length along ventral surface 8.75 mm, along dorsal surface 8 mm, width in mid­body 2 mm, anterior and posterior ends narrower, more so the latter. Colour uniformly yellowish­white. Dorsal surface slightly arched, invested in imbricating scales, which extend laterally and also ventrally. Sole distinct, enclosed within a groove that is displaced slightly to the right, extending from about 2 mm behind the mouth to terminate about 2 mm in front of the anus; covering membrane of sole damaged. Dorsal podia few, poorly developed, emitting between scales, restricted to the radii, about 10 per radius; sole bordered by larger podia, five on the right and three on the left; with the one on each end of the groove extremely well developed. Anal teeth minute.

Calcareous ring (Figure 14 H) simple, well calcified but delicate; radial plates triangular with an anterior, slightly bifid projection and a shallow depression for the retractor muscle, posterior surface slightly concave; interradial plates only slightly shorter but with deeper posterior concavity. Tentacles nine, of unequal length ­ five large, a single dorsal one of medium size, three ventral remarkably reduced; all tentacles finger­shaped (Figure 14 G) with minute lateral branches. Polian vesicle (Figure 14 H) single, tubular; stone canal remarkably short; madreporite poorly calcified, form difficult to determine. Gonad (ovary) (Figure 14 H) developed as two sacciform tubules attached to dorsal mesentery in anterior part of gut, each tubule full of ripe eggs. Retractor muscles originate from anterior third of longitudinal muscle bands.

Dorsal and lateral body wall covered with imbricating scales and much smaller perforated plates (Figure 14 A). Scales large, up 380 µm, single­layered, smooth, occasionally with 1–5 minute knobs; perforated plates, 150–220 µm (mean 180 µm), of irregular shapes, either smooth or faintly­knobbed and with up to 10 holes, commonly less, sometimes with one end slightly prolonged into a branched projection. Sole deposits small plates (Figure 14 B), 104–170 µm (mean 140 µm), perforated by 5–10 holes, similar in size and shape to those of dorsal body wall, but with nodules restricted to usually one side of plate which is devoid of handle­like projection. Dorsal podia densely packed with minute, 73–130 µm (mean 97 µm), plates and rods (Figure 14 C), usually with two or more perforations, occasionally none, endplates absent; ventral podia with endplates (ca 130 µm) (Figure 14 E) and other plates and rods (Figure 14 D) of similar size (69–125 µm, mean 97 µm) and shape as those of the dorsal podia. Tentacle deposits include mostly perforated rods (Figure 14 F) of varied form and size (54–170 µm, mean 94 µm).

Distribution

Type locality only.

Remarks

The single specimen represents a new species here referred to the monotypic genus E kkentropelma with E. brychia Pawson, 1971, as type species by original designation. The genus is characterised by a rigid U­shaped body form with a well­ defined sole that does not occupy the greater curvature of the body, hence mouth and anus lying in a plane perpendicular to the usual plane of bilateral symmetry, and sole deposits only buttons and no cups (Pawson 1971). Pawson states that the sole, although not occupying the greater curvature of the body, is still ventral in position with its centre in the mid­ventral radius. He, therefore, states that the mouth and anus are displaced, lying in a plane perpendicular to the plane, which contains the mid­ventral radius and the mid­dorsal interradius. In the type species some specimens had the sole displaced to the left while others to the right of the mouth­anus plane, making the sole functionally lateral.

In the present specimen the sole does not appear as distinct as in other psolids since it is deeply enclosed within a groove which is displaced to the right of the mouth­anus plane. The new species also differs from the type species in having dorsal podia arranged in a single series in each ambulacrum and very few marginal podia bordering the sole, and no cup­like deposits in the dorsal body wall. Further, the smaller plates of the body wall have smooth or slightly­knobbed margins but without projections described for the type species, and the gonad is developed as two sacciform tubules and not as tufts of tubules as in the type species. These differences clearly warrant a new species of Ekkentropelma, especially if we consider that the type species came from the Antarctic Peninsula, with depths in excess of 2000 m. With its single row of marginal podia the new species comes quite close to the preceding species but in its body form and some features of the sole deposits it is very different. According to Pawson, Ekkentropelma is closely related to Psolidium. However, besides this new species, the preceding one, and the southern African form erroneously referred to P. v i t re u m by Thandar (1999), it appears that no other psolid species has yet been described with a single row of marginal podia on each side of the sole.