They are dorsal and lateral outgrowths on the upper surfaces of the body.
The singular is ceras, which comes from the Greek word "κέρας", meaning "horn", a reference to its shape.
Cerata are also used, in some cases, for attack and defense. In many aeolid nudibranchs, the digestive system extends into the cerata. These nudibranchs eat stinging celled animals (Cnidarians) such as anemones, hydroids and sea fans or Portuguese men o' war. The stinging cells or nematocysts are passed unharmed through the digestive system to the tips of the cerata. Here the nematocysts mature and are then used by the nudibranch for its own defence.
In some nudibranchs, cerata are used as decoy tactics. Typically, these cerata are not armed with nematocysts, but when attacked, the nudibranch will autotomise or drop one or more of its cerata. The dropped cerata produce a sticky secretion and wriggle energetically for some time after being cast off, presumably causing a distraction and allowing the nudibranch to escape.
- BRUSCA, R.C. & BRUSCA, G.J. 2003 Invertebrates 2nd edition ISBN 0-87893-097-3
- http://www.seaslugforum.net/factsheet.cfm?base=phylmagn accessed 12 November 2009