(Bowerbank, 1874)
Species Overview
Hemimycale columella (Bowerbank, 1874) is an encrusting pale red-orange to pink sponge with very characteristic darker coloured rounded pore-areas, set off from the background surface by paler coloured elevated rims. It is slippery smooth to the touch and occurs in sublittoral kelp zones.
Taxonomic Description
Colour: Bright red to pale orange or pink. The darker coloured depressions have lighter coloured rims.
Shape, size, surface and consistency: Thin sheet to cushion. Several cm2 in lateral expansion. Moderately soft when alive and undisturbed. Surface slippery, smooth. It is covered in shallow, circular, non-contractile depressions of varying diameters. The rims of these are usually lighter coloured than the rest of the body. The depressions contain the inhalent pores (they are the pore-sieves ("cribles" in French) characteristic for the families Anchinoidae and Hymedesmiidae. The pore-sieves are covered by a fine, gauze-like, mesh. They become less obvious when the sponge is left out of the water. Oscules occur infrequently. They are located on top of special papillae which contract if disturbed and are lost on preservation. Contraction noticeable, in particular the oscules cease to be obvious when the sponge is removed from the water. The cushions tends to curl up at the edges when preserved. No smell.
Spicules: (Hemimycale columella spics) The megascleres are strongylostyles (i.e. strongyles with unequal ends) to subtylostyles, not differentiated into ectosomal and choanosomal spicules: 330-465 x 4-8 µm (Mediterranean specimens tend to have thinner and shorter spicules). There are no microscleres .
Skeleton: There is no special ectosomal skeleton, except at the pore-sieves, where the strongylostyles fortify the rims, and are tangentially arranged around the pores. The choanosomal skeleton is plumose and consists of loose tracts of spicules, which run vertically up to the surface, branching and anastomosing.
Cytology: (Boury-Esnault, 1972; Willenz, 1982) Two main types of cells with inclusions are found, spherulous cells and sacculiferous cells.
Calcium carbonate spherules (Vacelet et al., 1987): spherules of 2-55 µm in diameter were observed in preserved specimens from the Channel and the Mediterranean (Hemimycale spherules). Presumably, these were drawn as "gemmules" by Bowerbank (see drawing of Desmacidon columella ) (Desmacidon columella Bow.).
Choanocyte chambers: 35-40 µm, with choanocytes displaying a periflagellar sleeve.
Reproduction (Topsent, 1891a; Lévi, 1956): Eggs and embryos were observed in August and September at Roscoff, in April and October in the Mediterranean.
Ecology: Found on clean rock, stones or shingle. It attains its best development in the kelp zone. lt is not found in harbours.
Distribution: British Isles; France; Spain; Mediterranean. Not North Sea coasts. Northern limit probably is the west coast of Scotland.
Etymology: The name refers to the column-shaped type specimen.
Type specimen information: The type is in the Natural History Museum, London. MCS voucher: Mc1258, Rathlin Isl., Northern Ireland.
Remarks
Provided the colour is red-pink and the rims of the depressions are of a lighter colour, the identification stands a good chance of being correct, but in case of doubt microscopic examination is essential. Several other genera contain species which have depressions with rims which are the same colour as the general surface (see e.g. Phorbas fictitius) .
Sources: Forster, 1955; Ackers et al., 1985 (Editors: S.M. Stone, J.D. Guiterman, D. Moss); Van Soest et al., 1981; Hiscock et al., 1983: 26; Vacelet et al., 1987.