Diazona violacea is a species of tunicate, an ascidian in the family Diazonidae.

[4] This species is known from the northeast Atlantic from the British Isles to Portugal, and in the Mediterranean Sea.

In the British Isles it is found off Scotland, Ireland and SW England.

[3] It is a cold water species found below 30 m in Plymouth but as shallow as 15 m in Scotland.

The zooids are marked with white internal lines and circles and there are typically six spots around the exhalant siphon.