It is strong, thick, smooth and glossy, with inrolled edges at the sides of the long aperture on the underside.

Its normal habitat is living on gorgonians, or sea fans, at depths down to about 10 metres (33 ft).

[2] Simnia spelta is a specialist predator on gorgonians of the genera Eunicella, Paramuricea and Lophogorgia.

It feeds on the polyps and the coenenchyme, the living connective tissue that surrounds the horny skeleton, but does not graze excessively and therefore does not kill its host.

Eggs are laid on the branches of the host species and resemble the natural warty appearance of the stems.