Diazona violacea is a colonial ascidian forming massive colonies of up to 40 cm
in diameter and 20 cm in height. Young colonies are rather ball-shaped, whereas older ones are slightly
flattened. The zooids
are joined in a common gelatinous cushion-shaped base. The branchial parts of the zooids (the upper parts)
are distinct and emerge of 2 cm from the base. The test is more or less translucent, white or yellowish.
A vertical line draws the endostyle of each zooid; the atrial and oral siphons are underlined by a white
margin and six white spots ornate the upper part of the pharynx. Diazona zooids resemble clavelina ones but
their bases are different: a thick basal mass for Diazona versus a thin basal stolon for Clavelina.
At the end of summer, after reproduction time, zooids atrophy and there's only the basal mass left. In
spring-time, the colony buds again from this base.
It lives attached to rocks or stones covered by sand, in strong current-swept areas between 15 and 200 meters
deep in the Atlantic Ocean, the English Channel and the Mediterranean Sea.
Phylum Chordata, subphylum Tunicata, class Ascidiacea, order Phlebobranchia, family Cionidae, Diazona violacea Savigny, 1816.
Zooid: Individual, single animal.
Test: or tunic: thick layer secreted by the mantel containing cellulose and protecting the animal.
Oral siphon: Opening by which water is drawn in the ascidian.
Atrial siphon: Opening through which water is expelled.
Diazona violacea close-up view.
Photographs: © Javier Santiago. Published with author's kind permission.
Diazona violacea, Ria de Arosa, Galice, North-West of Spain. Depth 32 meters.
Text: Anne Bay-Nouailhat © 2007-2008.
Translation: Anne Bay-Nouailhat © 2007-2008.
