(Linnaeus, 1767)
Description
External appearance
Solitary. Body globular to ovoid, attached by base and up to 20 mm in diameter. Test thick and leathery, bearing radially branched spines.
Characters
Both siphons 4-lobed and placed at the top. From 12-16 branched branchial tentacles of variable size. Branchial sac with numerous rows of straight and transversal orientated stigmata; six branchial folds per side; eight longitudinal bars per fold. Gut left of branchial sac; stomach narrow and small, not marked off from the rest of the gut but with many diverticula forming a complex liver. One long and lobed gonad on each side (B. echinata morphology).
Habitat
Attached to hard substrata; from shallow water to depths of about 350 metres.
Distribution
Arctic-Boreal distribution.