Intraspecific aggression in the nudibranch Chromodoris annae Bergh, 1877: novel ‘fighting’ behaviour for the Chromodorididae (Gastropoda, Opisthobranchia)

This paper documents a bout of very aggressive behaviour between two individuals of Chromodoris annae witnessed by the author subtidally in Timor-Leste in August 2010. Pugnacious behaviour has been observed and recorded previously in two other families of anthobranch (= dorid) nudibranchs, viz. Polyceridae (one genus only) and Gymnodorididae (two genera at least), both phanerobranch families where cannibalism of conspecifics is an extension of predation on other anthobranch dorids. Pugnacious behaviour has apparently never previously been recorded in the Chromodorididae, the largest family of cryptobranch dorids. Although the observed aggression was certainly not cannibalistic, it is uncertain whether it was related to mating or feeding, or had some other purpose.