Host defence mechanisms in marine invertebrate larvae

Invertebrate immunity has been extensively investigated in adult animalsfrom most phyla, however, very little is known of defence mechanisms in larval invertebrates. Existing information has established that motile phagocytic cells are present in the veliger larvae of bivalves and that the pluteus larvae of echinoderms possess antibacterial substances. Antimicrobial and cytotoxic activities have also been found in the eggs of opisthobranch molluscs, but have yet to be described in the larvae. Chemical defences, which may have antimicrobial or cytotoxic capabilities in addition to anti-predatory purposes, have been recorded from zoanthid, echinoderm and tunicate larvae. Many other aspects of immunity remain to be investigated in invertebrate larvae, and additional methods need to be developed for easier recognition and quantification of the larval immune response. The marine mussel, Mytilus edulis, is a species of particular importance, from both economic and ecological viewpoints. A disaggregation technique has been tested by the authors on M. edulis larvae and used to show that the larval cells possess certain enzymes associated with adult mussel haemocytes and are capable of phagocytosis.