Chemical Defence in Cephalaspidean Gastropods: Origin, Anatomical Location and Ecological Roles

Within the opisthobranchs, the cephalaspideans are traditionallyconsidered atransitional group between typical testacean prosobranchsand shell-less opisthobranchs. Thecephalaspidean anatomy, includingthe presence of a cephalic shield, is related to burrowingthroughsoft sediment. Recent studies have shown that some herbivorousand carnivorouscephalaspideans contain secondary metabolites.The micro-herbivorous bubble snails of theBullidae and Haminoeidaefamilies are known to have secondary metabolites which havedifferentecological roles. The polypropionates isolated from Bulla gouldianaand B.striata were deterrent to fishes while the secondarymetabolites of Haminoeacallidegenita, H. fusari, H. hydatis,H. navicula, H.orbignyana and H. orteai were alarm pheromonesemployed during crosscopulation. In Bulla gouldiana and B.striata, the defensive secretion waslocated mainly in a whitegland along the margin of the mantle. In Haminoea species,alarmpheromones were located in external parts (cephalic shield,parapodial lobes and posteriorpallial lobe). The carnivorous cephalaspideans Navanax inermis and Philinopsisdepictaemploy chemotaxis to follow the slime trail of theirprey, which include other cephalaspideans oreven congenericindividuals. N. inermis and P. depicta sequester alarmpheromonesand allomones from their cephalaspidean prey, which are ejectedwhen N.inermis and P. depicta are disturbed. The specific metabolic patterns of Mediterranean cephalaspideanssuggest that these patternscan be used as chemotaxonomic markers.We propose the use of a single Thin LayerChromatography todifferentiate among Mediterranean Haminoea species. (Received 3 February 1997; accepted 22 May 1998)