Metabolites of Marine Opisthobranchs: Chemistry and Biological Activity

Opisthobranchs are marine gastropod molluscs, the shell of which is either reduced or completely absent. Many chemical studies have been performed in order to investigate their surprising immunity from predators. An annual summary of the chemical liter- ature on marine organisms is provided by Faulkner (e.g. 2000) and includes studies of opisthobranch molluscs. The same author also discussed their chemical defense (Faulkner, 1992). Ecological aspects were discussed, first by Karuso (1987), and then by Cimino and Sodano (1989) for nudibranchs, by Carefoot (1987) and by Yamada and Kigoshi (1997) for anaspideans. Faulkner and Ghiselin (1983) were the first to link chemistry of opisthobranchs to evolution; more recently, evolutionary aspects were also discussed by Cimino and Ghiselin for sacoglossans (1998) and dorid nudibranchs (1999). Biosynthetic studies were summarized by Cimino and Sodano (1993), by Garson (1993) and by Davies-Coleman and Garson (1998). Dietary relationships with sponges were reviewed by Cimino and Sodano (1994), and finally, very recently, a complete overview of the chemistry and ecology of sacoglossans and dorids was published (Cimino et al. , 1999). Monographs and faunas (Thompson, 1976; Riedl, 1983; Sabelli et al. , 1990) give somewhat different classifications of the Opisthobranchia. In this paper, as well as in our last review (Cimino et al. , 1999), we have followed the classification recently pro- posed by Rudman and Willan (1998), which is outlined in Figure 15.1. According to this arrangement, opisthobranchs are split into nine orders: Cephalaspidea, Anaspidea, Notaspidea, Sacoglossa, Nudibranchia, Acochlidea, Rhodopemorpha, Thecosomata and Gymnosomata. The main orders are the first five. In this paper we will present a general overview of the chemistry for Cephalaspidea, Notaspidea and Anaspidea. On the other hand, our review of Nudibranchia continues Karuso's coverage (1987) but excludes dorids, recently discussed (Cimino et al. , 1999) along with species belonging to the Sacoglossa. The pioneer chemical studies of Gymnosomata will be reported here. As in the previous review, general morphological and biological descriptions of the different groups of opisthobranchs have been reported here following Beesley et al. (1998)