The nudibranch, or sea slug, is one of my favourite animals to spot underwater. They are often colourful little creatures, advertising their toxicity to predators.
You find nudibranchs around the world, in temperate and tropical seas, and even in the Antarctic. They are hermaphrodites: possessing both male and female organs. Some lay a single string of eggs, others produce coiled flat ribbons. These are usually white but may be red, pink, orange or other colours.
The nudibranch we're featuring today, Coryphella browni, has a translucent white body and numerous pretty coloured pointy projections (cerata), with white tips, on its back.
It feeds on hydroids, which are simple stinging-cell animals related to corals and sea anemones. It not only doesn't mind their stinging cells, it actually puts them to use. The nudibranch passes the intact cells through its digestive tract and out to the cerata tips. Any animal taking a bite out of the cerata will cause the stinging cells to discharge, then give up and go and eat something less painful.
Coryphella browni is up to 5 cm long and occurs around the British Isles and Northern Europe. Its egg masses are laid in a wavy spiral near its hydroid food.
Great British Marine Animals, by Paul Naylor, Deltor (2005)
Dive sites and marine life of the Calf of Man and neighbouring area by Bill Sanderson, Bruce McGregor and Andrew Brierley, Immel Publishing Ltd, 1994, Paperback.
The Underwater Photographer: Digital and Traditional Techniques, by by Martin Edge, Paperback, 536 pages (2009)