CURRENTLY ACCEPTED NAME is Catriona aurantia (Alder & Hancock,1842) . The true C. gymnota (Couthouy, 1838) lives in the NW Atlantic and is not the species here described.
Body (excluding appendages)
Up to 22 mm long. Translucent white, sometimes delicately tinted orange or rosy. No surface markings.
Often conceal sides and much of dorsum of body [image8]. Arranged in rows on each side of the body. Translucent white revealing coral pink  to reddish brown  or yellow-olive  internal digestive gland. Wide band of powdery white , yellow and/or orange surface pigment covers distal end, except translucent white tip containing cnidosacs. The powdery area may be bicolored orange and white .
Smooth. Translucent, tinted orange-brown . No surface pigment.
Translucent white oral tentacles. No surface pigment .
Slight rounded swelling at anterior, no propodial tentacles. Translucent white sole .
- Rhinophores not tinted orange-brown
- Cerata more numerous, extend forwards to rhinophores.
- Powdery pigment on cerata less extensive.
- White surface pigment often on rhinophores and oral tentacles.
- Usually (but not always) on Hydractina echinata on shell of Hermit crab.
LWS rocky shores and shallow coastal waters where strong currents. At or near base of its prey; Tubularia spp. (EML). Hermaphrodite. White spawn mass laid in transparent kidney shape case at base of Tubularia. Attached by broad stem on one side. Before release, moving hatched white veliger larvae visible within case . Transparent larval shell reflective, usually with two mobile bright highlights which can iridesce green. Veliger larvae swim in plankton for up to ten days before transforming into the adult form. Breeds most months. Several generations each year.
Western Mediterranean to Norway (GBIF map). Common all round Britain and Ireland on hard substrate sea beds, and occasionally on rocky shores, where Tubularia occurs.
The map provided here shows the distribution of the species based on Conchological Society data.
Distribution data for the species in the UK based on a range of other sources can be found on the UK National Biodiversity Network (NBN).