Description: A large colonial ascidian, forming globular colonies. Smaller colonies are spherical, larger ones squat, with a small basal attachment. The test is transparent, with a greenish tinge when out of water. The zooids are large, with white markings similar to Clavelina lepadiformis. This marking consists of a white line along the endostyle, dorsal lamina and around the top of the branchial sac, and six small white spots around the atrial siphon. 50-400mm diameter colonies.

Habitat: Typically a deep water form with a preference for clear offshore water, quite common in Scottish west coast waters inshore in the Oban/Mull area. Usually on rock ledges or stable boulders in current-swept areas. 20-200 m depth.

Ecology: Diazona reproduces sexually during the summer and degenerates in August/September into a hard globular resting bud. Individual zooids divide in this bud to each produce 8 new zooids when growth begins again in January.

Distribution: West and south coasts of the British Isles, quite common in west Scotland, in offshore locations in W. Ireland and occurring as far south as Spain and the Mediterranean.

Similar Species: Only Clavelina lepadiformis has similarly marked zooids, but that species does not have a massive common test, the zooids are only joined at their bases. Diazona is larger and the six small white spots around the atrial siphon are diagnostic.

Key Identification Features:

• Large globular test with white-marked transparent zooids.
• Six small spots around atrial siphons.

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

iNaturalist: Diazona violacea at iNaturalist World Species Observations database.

WoRMS: Diazona violacea at World Register of Marine Species. Accepted name: Diazona violacea Savigny, 1816. AphiaID: 103733.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Aplousobranchia; Diazonidae; Diazona