Rhizaxinella elongata

(Ridley and Dendy, 1886)

Species Overview

Rhizaxinella elongata (Ridley and Dendy, 1886) is a yellowish grey, stalked, oval, solid sponge with a finely hispid surface and firm consistency. It is a deep water species recorded from the North Atlantic and the Mediterranean.

Taxonomic Description

Colour: Yellowish grey.
Shape, size, surface and consistency: Oval body on a thin stalk, which is attached to the substrate by a root-like support system. Body solid, elongated, up to 6 cm long, 1 cm wide; stalk up to 3 cm long, 0.5 cm wide. Surface finely hispid.
Spicules: (Rhizaxinella elongata spics) Styles and tylostyles, long, smooth, in three categories: long styles: 1750-2000 x 14-16 µm, intermediate styles: 500-2000 x 5-6µm, and small tylostyles: 200-400 x 3-6 µm.
Skeleton: Ectosomal : bouquets of small tylostyles, among which the endings of intermediate styles are found. Choanosomal : intermediate styles radiating from the centre of the oval body towards the surface. Stalk : long styles arranged in parallel tracts.
Ecology: Deep water, from 90 m downwards.
Distribution: Roscoff, English Channel; Mediterranean, Azores.
Type specimen information: The type is in the Natural History Museum, London.

Remarks

The solid body on a stalk in combination with the spicules is distinctive. A second species, R . pyrifera , occurring in the Mediterranean and the adjacent Atlantic, differs in having trichodragmas.
Source: Topsent, 1900.