Photo copyright Tim Nicholson.
Sea squirt, Corlla parallelogramma Taken on the wreck of the Stassa, Scotland.
A small, solitary, species with an almost transparent tunic. The internal organs are visible. Up to 5 cm tall. Sea squirts, or tunicates, are members of the Chordata phylum - the major animal group that contains fish, birds and mammals.
Great British Marine Animals, by Paul Naylor, Deltor (2011)
The Underwater Photographer: Digital and Traditional Techniques, by by Martin Edge, Paperback, 536 pages (2009)