Colonies 10-30 cm across. Zooids soft, translucent, with a pale green tinge. The bases of each zooid are embedded in a common basal mass.

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. 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.

Adriatic Sea, East North Atlantic, European waters (ERMS scope), Greek Exclusive Economic Zone, Irish Exclusive economic Zone, Scotland, United Kingdom Exclusive Economic Zone, West Coast of Ireland, West Coast of Scotland

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.

Depth range based on 28 specimens in 1 taxon.
Water temperature and chemistry ranges based on 13 samples.

Environmental ranges
  Depth range (m): 0 - 44.5
  Temperature range (°C): 10.625 - 11.851
  Nitrate (umol/L): 5.669 - 8.618
  Salinity (PPS): 35.229 - 35.352
  Oxygen (ml/l): 6.013 - 6.153
  Phosphate (umol/l): 0.414 - 0.574
  Silicate (umol/l): 2.442 - 2.990

Graphical representation

Depth range (m): 0 - 44.5

Temperature range (°C): 10.625 - 11.851

Nitrate (umol/L): 5.669 - 8.618

Salinity (PPS): 35.229 - 35.352

Oxygen (ml/l): 6.013 - 6.153

Phosphate (umol/l): 0.414 - 0.574

Silicate (umol/l): 2.442 - 2.990
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

 Sublittoral attached to a variety of substrata, mostly adjacent to deeper waters.

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.

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.