Mollusca
Mollusc's reproductive organs are situated in the visceral mass. 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.
Mussels have 2 separate sexes, (both having male and female sexes) and they are called
hermaphrodites. These bivalves reproduce by releasing eggs and fertilization happens externally. The sperm in the water fertilizes these eggs forming a planktonic larval stage.
The spawning varies depending on the temperature and is usually happens from April
to November and after being hatched in time the swim freely and after several weeks these larvae settle to the seabed as a mature mollusk.
hermaphrodites. These bivalves reproduce by releasing eggs and fertilization happens externally. The sperm in the water fertilizes these eggs forming a planktonic larval stage.
The spawning varies depending on the temperature and is usually happens from April
to November and after being hatched in time the swim freely and after several weeks these larvae settle to the seabed as a mature mollusk.
"Prosobranch" Snail
In some other species like the "prosobranch" snail, both have 2 sexes and reproduction occurs by spraying the eggs and sperm into the water but fertilization may happen or not and it's a matter of chance.
The Squid
The reproduction the squid starts when a male squid produces a special arm called a hectocotylus that transfers male sperm to the female squid through her pallial cavity. Once fertilized the female later laysa number of eggs that will hatch into a small squid larvae. The cephalopods are highly protective of their young ones. They take care of them by cleaning, feeding and defending them from the attackers or threat of danger to the extent that female squid could die because they can't defend themselves because they are too weak.