ABSTRACT
In mollusca, the hormone system is perhaps most diverse of all invertebrate phyla, as it differs not only between classes but also within classes reflecting extreme differences in sexuality and life history patterns (e.g. Oekten et al., 2004). Remarkably, 25% of molluscs are simultaneous and sequential hermaphrodites; some of these Simultaneous Hermaphrodites (SH) are capable of selfing. However, hardly a few publications are available on endocrine differentiation in protandric (e.g. Crepidula fornicata, Le Gall et al., 1981), unilateral SH (e.g. Aplysia californica, Zhang et al., 2000, 2008, A. depilans, Lupo di Prisco and Fugheri, 1975) and reciprocal SH (e.g. Lymnaea stagnalis, De Jong-Brink et al., 1981). Surprisingly, a host of vertebrate-types steroids is present in molluscs but their endogenic biosynthesis and role in reproductive cycle is questioned (Scott, 2013). Only, a single publication by Wang and Croll (2004) reports sex reversal in scallop Placopecten magellanicus treated with one or other steroid. Whereas pollutants like tributyltin (TBT) masculinize (female) fishes, it only superimposes masculine traits on female gastropods. Many molluscs serve as intermediary host to trematode parasites, which either partially or completely sterilize them.
