Hamacantha falcula

(Bowerbank, 1874)

Species Overview

Hamacantha falcula (Bowerbank, 1874) is an irregularly lobate, cushion-shaped sponge with a detachable skin. The oscules are slightly raised on low conules. Live colour has not been recorded. It is a deep-water sponge. The genus Hamacantha has characteristic microscleres (diancistras); the present species may be distinguished from the two other Hamacantha species from the area by its possession of toxas.

Taxonomic Description

Colour: Live colour unknown; yellow to white in alcohol.
Shape, size, surface and consistency: Massive, irregularly lobate, roundish. Size up to 9.5 cm in lateral expansion. Surface smooth, with detachable "skin". Oscules on low conules of several mm high. Consistency rather firm.
Spicules: (Hamacantha falcula spics) Megascleres : Styles 340-470 x 5-8 µm.
Microscleres : Diancistras in three categories: 100-178 µm, 30-57 µm and 18-28 µm; toxas 60-157 µm.
Skeleton: Ectosomal skeleton a tangential reticulation of spicule tracts. Choanosomal skeleton plumose, with spicule bundles running to the surface where they fan out.
Ecology: Deep water: 85-2280 m
Distribution: Roscoff, W Ireland, Scotland, Sweden, Norway, Faroes, Iceland; also Madeira and Azores.
Etymology: Falcula (Latin) = small sickle, referring to the shape of the microscleres.
Type specimen information: The type is in the Natural History Museum, London: Type: BMNH 1910.1.1.191 (dry). Norman Collection.

Remarks

Hamacantha with its characteristic diancistras is represented by three species in the area. H . johnsoni has oxeas for megascleres and true sigmas; H . papillata (=H . implicans ) has trichodragmas and only a single category of diancistras. Both species lack the toxas of H . falcula .
Source: Arndt, 1935.