About 40 red C. nana feeding abreast on Hydractinia echinata coating a metal rail and leaving spawn behind as they progress.
Like other nudibranchs, C. nana is a simultaneous hermaphrodite. A convoluted ribbon of spawn (enlarged in inset) is laid on or near H. echinata.
Shipwreck on Dogger Bank, North Sea. July 2012. © Niels Schrieken