Defensive glandular structures in opisthobranch molluscs : From histology to ecology

Opisthobranch molluscs are an extremely interesting group of animals, displaying a wide diversity in shape, colour and life strategies. Chemical ecology of this group is particularly appealing since most species have a reduced or absent shell and have developed chemical defences to avoid predation. New results on defensive glandular structures as well as a compilation of literature data in sea slugs (Opisthobranchia, Gastropoda, Mollusca) are presented in this review. Investigation of these structures is based on detailed analyses of the histology of many representative species of all major taxa of the Opisthobranchia. The results are correlated with previous and new findings of secondary metabolites in these animals and are set in a phylogenetic context. Additionally, information on food sources is given. Also, an hypothetical scenario relating chemical ecology to histology is proposed. This information will help future analyses to investigate defensive devices on a much more accurate basis and allow a better understanding of evolutionary processes, which are observed independently in many opisthobranch clades.