Thetys vagina is a thaliacea of up to 30 cm long. Like many other Thaliacea, it is
pelagic and has two
forms: an asexual solitary form, the oozooid, which buds and develop into a colony of sexual individuals,
the blastozooids. Thetys vagina is oblong and the two siphons are opposite, at each end of the body. The
oral siphon is broad. The atrial siphon is framed by a pair of long dark outgrowths which are absent in the
colonial form. Through the translucent body, muscular bands and a dark round spot formed by the gut and called the
nucleus, are clearly visible. Muscular bands ensure locomotion and food (phytoplankton) entry by pumping
water in. Solitary
animals possess 20 muscular bands that uncompletely surround the body whereas colonial individuals
have only 5 muscular bands (see photograph showing a blastozooid separated from the rest of the colony).
Colonies are composed of an aggregate of individuals organized in a double-chain of sometimes
several meters long.
This is a cosmopolitan pelagic species that can be encountered from surface to 150 meters deep in the Atlantic Ocean, the Mediterranean Sea, as well as in the Pacific Ocean and the Indian Ocean.
(source : European Register of Marine Species)
Oral siphon : Opening by which water is drawn in the ascidian.
Atrial siphon : Opening through which water is expelled.
Top photograph :
© Pascale Sentenac. Published with author's kind permission :
Thetys vagina, blastozoïde separated from the colony, Port Cros, South of France. Depth 20 meters.
Bottom photograph : © Graham Owens. Published with author's kind permission :
Thetys vagina, Solitary asexual specimen. Garachico, Tenerife, Canary Islands. Depth 20 meters.
Text : Anne Bay-Nouailhat © 2006-2017.
Translation : Anne Bay-Nouailhat © 2007-2017.