Feeding preferences of Oxynoe olivacea (Opisthobranchia : Sacoglossa) among three Caulerpa species

摘要

The opisthobranch order Sacoglossa (Ascoglossa) is a relatively widespread group of stenophagous sea slugs comprising about 250 species. Sacoglossan are deemed as marine specialist herbivores and are often among the rarest components of inshore communities being strongly entrained upon the life histories of their algae. The close association between these molluscs and their food algae has invoked terms such as co-evolution and provides a fascinating biological puzzle, distinct from other photosymbiotic associations in several ways. Moreover, physiological adaptations as functional kleptoplasty (= chloroplast symbiosis) and the capability of taking up and concentrating secondary metabolites from the algal food have been described. The majority of species feed upon siphonalean green algae, and the stenophagy is is plesiomorphic, feeding being restricted to the green, siphonalean algal genus Caulerpa fogr the entire suborder Oxynoacea. The most representative species in the Mediterranean is the endemic Oxynoe olivacea (Rafinesque, 1819) characterized by small size (20 mm long), an extreme host-specificity, a cryptic coloration and a planktotrophic veliger larvae.