Spanioplon armaturum (Bowerbank, 1866)


Family : Hymedesmiidae

Form: Moderately thin sheets, up to 7cm across, to cushions 1cm thick.

Colour: Grey (dark red brown when dried).

Smell: None. Slime : "Slimy".

Consistency: Soft.

Surface: Smooth, with obvious exhalent canals which become deep grooves on removal from the water. "Uneven, hispid, in places slightly conulose".

Apertures: Oscules few in number, sometimes scattered, or at the edge of specimens growing on shells. Ostia not apparent.

Contraction: Considerable contraction and collapse of the oscular channels occurs on removal from water.

Internal characters

Skeleton: The ectosome consists of tangentially arranged strongyles, sometimes collected into bundles. In the choanosome there are styles loosely arranged into tracts, together with many scattered small acanthostyles.

Spicules: There are three types of megascleres. The styles (a) measure 235-(250)-260Ám "220-250Ám" by 2-8Ám, and are slightly curved. The heads of some show tylote and/or mucronate tendencies, and very sparse spines may occur towards the head end. Strongyles (b) measure 195-(200)-205Ám by 1-8Ám, and sometimes possess variably and unequally dilated ends. The acanthostyles (c) are 55-(72)-90Ám "40-65Ám" by 1-5Ám, and they are characteristically small and thin, with only slightly swollen heads, and very short points. They are weakly, but entirely, spined. Microscleres are absent.

Habitat: 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 50m.

Distribution: N. Atlantic, Mediterranean. Known recently from Lough Hyne, Strangford Lough, several localities in the Channel, St. Kilda.

Distribution Map: NBN map : National Biodiversity Network mapping facility, data for UK.

Identity: 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.

Voucher: BELUM : Mc211. Strangford Lough, Down.

Editors: D. Moss, B.E. Picton.

 Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. [In] Sponges of Britain and Ireland