Reproduction

Mollusc's reproductive organs are situated in the visceral mass (refer to female squid picture). Both simple and highly complex forms of sexual reproduction are inhibited. Egg fertilization occurs externally (except most belonging to the class Cephalopoda), sometimes in broadcast spawning (large egg and sperm quantities released in water at the same time). Molluscs are protostomes, they have spiral cleavage and require separate sexes for reproduction. Some can be hermaphrodites, for example snails because of their slow movement they have the ability to change sexes. After the egg is fertilized, it becomes a larva, which is motile. This is called a trochophore larva. When this later elongates in the next developmental stage it is called a veliger larva.