Description: Colonies consist of small club-shaped heads with narrow stalks arising from a creeping stoloniferous base. The test is transparent and the zooids can clearly be seen. Individual zooids are pigmented extensively with white on the endostyle, the branchial bars, the upper edge of the branchial sac, the bases and the extreme tips of the 8 lobes of the oral siphon. They are usually arranged in a single series of 6-12 zooids around a common exhalant opening. 10mm tall x 5mm diameter of head.

Habitat: From the lower shore to 200 m but typically a member of the exposed sublittoral fringe/shallow infralittoral communities. Commonly found on steep rock faces but also on stones, algae, etc.

Ecology: Fully-developed tadpole larvae are released from the colonies, which probably grow up in spring from overwintering stolons.

Distribution: There are apparently no records from the east coast of England but otherwise the species is widely distributed around the British Isles, and from Scandinavia to the Mediterranean.

Similar Species: Sidnyum elegans also has 8 lobed oral siphons with white pigmentation but forms large broad-based colonies. Several other polyclinids are similar.

Key Identification Features:

• 8-lobed oral siphon.
• White pigmentation of zooids.
• Small clumps of zooids.

Distribution Map from NBN: Sidnyum turbinatum at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Sidnyum turbinatum at iNaturalist World Species Observations database.

WoRMS: Sidnyum turbinatum at World Register of Marine Species. Accepted name: Aplidium turbinatum (Savigny, 1816). AphiaID: 103670.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Aplousobranchia; Polyclinidae; Sidnyum