The egg-laying behaviours of the gastropod mollusks

Mollusca is the largest marine, phylum about 23% of all the named marine organism.1 The gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca according for 80% of total mollusca.2 Fresh water gastropods are divided in to two subclasses, Prosobranchia and Pulmonata. Most of the species associated as intermediate hosts of helminthes parasite.3,4 Planorbidae and Limnaedae colonized in freshwater habitat because they have broad physiological and ecological concepts. The anatomy, behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another. Therefore, it is difficult to state many generalities for all gastropods. Observation showed that the snail population and frequency of infection greatly varies from place to place and seasonally. The snail has to respond against environmental change. The first review of reproduction in fresh water pulmonates are pointed by Duncan5 later on Geraets & Joose.6 Among pulmonates hermaphroditism is universal and almost universal among ophisthobranche gastropods but rare in all other gastropods.7 The hermaphroditism means adult has both female and male functioning system but it is not necessary that individual engages both sexual function in any single mating.7 Aquatic gastropods generally deposite their eggs in gelatinous capsule that are attached to surface or aquatic plant leaves. The self fertilization in pulmonates was first noted by.8 The gonad is called ovotestis/ gonadal tissue and sperm are passed through via duct in to vesicular seminal. The release of ova from the gonads is controlled by hormone at least in the ophisthobranch and basometophoran pulmonates and may be land snail.7 The endocrine gland secrete these hormone have been characterized in Lymnaea and Aplysia.7 The caudodorsal cells are present in cerebral ganglion and release two ovulation hormone. Abiotic factors increases the rate of reproductive capacity.9 Srivastava et al.10 reported significant positive correlation between acetyl cholinesterase and egg laying in Lymnaea acuminata a fresh water pulmonates. The aim of the present review is demonstrate the role CDCs cells, their structure and mechanism involve in reproduction behavior of pulmonates.