(Bowerbank, 1866)
Species Overview
Spanioplon armaturum (Bowerbank, 1866) is a greyish thinly encrusting to cushion shaped sponge with an irregular grooved surface. Consistency is soft. Microscopic examination is necessary for a positive identification. It is found along all coasts of Europe.
Taxonomic Description
Colour: Grey (dark red brown in alcohol and when dried).
Shape, size, surface and consistency: Moderately thin sheets, up to 9 cm across, to cushions 1 cm thick. Surface smooth, with obvious exhalent canals which become deep grooves on removal from the water; uneven hispid, in places slightly conulose. Oscules few in number, sometimes scattered, or at the edge of specimens growing on shells. Ostia not apparent, but probably in "micro-"areolae. Considerable contraction occurs on removal from water. Slimy. Consistency soft.
Spicules: (Spanioplon armaturum spics) (Hymedesmia stephensi) There are three types of megascleres . Tornotes measure: 165-225 x 1-8 µm, and often possess variably and unequally dilated ends. The styles measure: 205-310 x 2-8 µm, and are slightly curved. The heads of some show tylote and/or mucronate tendencies, and sparse spines may occur towards the head end. The acanthostyles (Spanioplon armaturum acst) are: 40-95 x 1-5 µm, and they are characteristically small and thin, with only slightly swollen heads, and very short points. They are entirely, spined. Microscleres are absent.
Skeleton: The ectosome consists of tangentially arranged tornotes, sometimes collected into bundles. In the choanosome there are styles loosely arranged into tracts, together with many scattered small acanthostyles.
Ecology: On stones, bivalve shells, and under boulder/bedrock overhangs. Found both in very sheltered conditions in sites like Strangford Lough, in Modiolus communities, and on very exposed bedrock, eg. at St. Kilda. In the Mediterranean, reported on bryozoans, other sponges, and plant debris. Shore to 50 m.
Distribution: Norway, St. Kilda, S England, Ireland, W coasts of France and Spain, Mediterranean.
Etymology: The name refers to the acanthostyles.
Type specimen information: The type is in the Natural History Museum, London: BMNH 1930.7.3.125 (dry), Strangford Lough. MCS Voucher BELUM Mc211, Strangford Lough, N Ireland.
Remarks
The size and shape of the acanthostyles, and the variability of the other two megascleres, are characteristic on microscopic examination. This sponge typically covers shells of Chlamys varia and develops into thick cushions completely covering the shell, with a single oscule at the outer edge. It is frequently perforated by many tubes of polychaete worms.
Source: Ackers et al., 1992; Van Soest, 1987.