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(Bowerbank, 1864)

Species Overview

Hamacantha (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. (Vomerula) falcula has toxas; H. (Hamacantha) papillata (=H. implicans) has trichodragmas and only a single category of diancistras. Both species have styles instead of the oxeas of H. (H.) johnsoni.
Source: Arndt, 1935.

Hamacantha johnsoni