Description: Moderately thin sheets, up to 7cm across, to cushions 1cm thick. Grey (dark red brown when dried). Soft. Oscules few in number, sometimes scattered, or at the edge of specimens growing on shells. Ostia not apparent.

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 from NBN: Spanioplon armaturum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Spanioplon armaturum at iNaturalist World Species Observations database.