C. pellucida occurs along the Mediterranean coast of Spain and France, and along the Atlantic coast of Iberia. It has been in Brittany, France, at least since 2002 (Poddubetskaia, 2002). It extended its distribution to Cornwall, England where it was first recorded in 2012 and became established there and in Devon in the subsequent decade. It is sometimes locally common.
Sublittoral, Coverack, Cornwall, 16 September 2012. First known record in Britain of C. pellucida. © D. Kipling