Predation by the nudibranch Tritonia odhneri (Opisthobranchia: Tritoniidae) on octocorals from the South Atlantic Ocean

The diet of the nudibranch mollusc Tritonia odhneri was investigated for the first time based on a detailed anatomical analysis of the gut content of 52 specimens. Digestive tracts of specimens were analysed under stereoscopic microscope equipped with digital camera. Portions of octocorals containing the calcareous sclerites were removed from the tracts and prepared for scanning electron microscopy (SEM). Sclerite morphology and size were determined at the species and genus level on the basis of a taxonomical revision and compared with fresh octocoral specimens collected from Patagonia (San Jorge Gulf) and with voucher specimens from the collections of Museo Argentino de Ciencias Naturales (MACN-in). Specific predation of T. odhneri on octocoral species present in the southwestern Atlantic Ocean was detected. The nudibranch feeds on the gorgonians Primnoella divaricata, Primnoella scotiae (=P. compressa) and Tripalea clavaria, and the pennatulaceans Renilla octodentata and Stylatula sp. A world checklist of dietary interactions between species of the genus Tritonia and octocorals is presented and discussed.