Hexadella racovitzai

Topsent, 1896

Species Overview

Hexadella racovitzai Topsent, 1896 is a pale rose, finely conulose encrusting sponge, related to Aplysilla but differing from it in the absence of any fibres. It is a Mediterranean species recorded once from Roscoff.

Taxonomic Description

Colour: Rose-coloured, with light yellowish tinges.
Shape, size, surface and consistency: Thickly encrusting. Lateral expansion may be considerable, but thickness not exceeding 5 mm. Surface smooth but demonstrating conulesa arranged in paralallel ridges, similar to Aplysilla or Darwinella . The "skin" may be rather easily peeled off and has a characteristic reticulate appearance. Consistency soft.
Spicules: Absent.
Skeleton: Absent. The skin is collagen-reinforced, and may act in some measure as external skeleton but otherwise the body is unsupported, with many channels and lacunae.
Choanocyte chambers: Large and sac-shaped, 65-75 µm in length (histological preparation necesary).
Ecology: On rocks, on pebbles, in deep water 9-85 m (Roscoff: 60 m).
Distribution: Mediterranean, Roscoff, Canary Islands.
Etymology: Named after Topsent's friend Mr. E.G. Racovitza.
Type specimen information: Presumably in the Muséum National d'Histoire Naturella, Paris.

Remarks

This is a typical Mediterranean species, recorded only once from the west coast of France. It resembles Aplysilla or Darwinella , but is easily distinguished from them by the absence of any skeletal structures. Other such species are Chondrosia reniformis , but this is shiny-smooth and has a distinct cortex, Oscarella lobularis , but this has a lobulate surface, and Halisarca dujardini , but this has a smooth punctate surface. None of these species has conules nor are they rose-coloured.
Source: Topsent, 1896.