Pilgrim Hervia - Cratena peregrina - Colourful Cerata against a Dark Reef

A Pilgrim Hervia clings to a hydroid-covered reef, its vivid orange-red cerata and bluish tips standing out against the dark background.

The Pilgrim Hervia (Cratena peregrina) is a slender aeolid nudibranch with a translucent milky-white body, long oral tentacles and bright orange rhinophores. Numerous elongated cerata are arranged in clusters along the back, displaying orange to reddish digestive glands and distinctive violet or bluish tips. These cerata function partly in respiration and also contain branches of the digestive system. The species is commonly associated with rocky substrates carrying hydroid colonies, particularly Eudendrium, on which it feeds. It occurs throughout the Mediterranean and parts of the eastern Atlantic, generally in shallow coastal waters, and commonly grows to about 3–5 centimetres in length.