Hamacantha johnsoni

(Bowerbank, 1864)

Species Overview

Hamacantha johnsoni (Bowerbank, 1864) is a thickly encrusting deep-water sponge with smooth but irregular surface and detachable skin. Live colour has not been recorded. 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 oxeas as megascleres instead of the usual styles.

Taxonomic Description

Colour: Live colour not recorded; yellowish in alcohol.
Shape, size, surface and consistency: Massively encrusting, with irregular but smooth surface; oscules on conical elevations. Size up to 4 cm in lateral expansion. The "skin" is easily detachable. Consistency fragile.
Spicules: (Hamacantha johnsoni spics) Megascleres : Oxeas, gradually tapering, with sharp points: 450-600 x 8-10 µm.
Microscleres : Diancistras in two distinct size categories: 100-160 µm and 30-55 µm; true sigmas (not diancistra-like): 20-25 µm.
Skeleton: Ectosomal : a tangential reticulation of spicule tracts. Choanosomal : plumose tracts traversing the interior fanning out at the surface; large subdermal lacunae.
Ecology: Deep water, 50-1300 m, on corals and shells.
Distribution: Norway, W Ireland; also Azores and Madeira.
Etymology: Named after Dr James Yate Johnson of Madeira.
Type specimen information: The type is in the Natural History Museum, London: Unregistered slide from Type (Bk 1184), also slide Bk 1103.

Remarks

This species was originally described from Madeira, with a few lines only, but subsequently was found off the coasts of NW Europe.
Hamacantha with its characteristic diancistras is represented by three species in the area. H . falcula has toxas; H . papillata (=H. implicans ) has trichodragmas and only a single category of diancistras. Both species have styles instead of the oxeas of H . johnsoni .
Source: Arndt, 1935.