Mollusca
Mollusca is a phylum of species that range from the cuttlefish to the sea snail. Species in the mollusca phylum reproduce either through external or internal fertilization. Internal fertilization occurs when the species functions as both sexes and is thus a hermaphrodite. External fertilization occurs when there are two separate sexes and a sperm cell unites with an egg cell. Both of these processes require a very complicated reproductive system.
Octopus
The Octopus reproduces through external fertilization were there are both male and female sexes. A male's reproductive system consists of a meter long arm called the hectocotylus that it uses to insert it's spermatophores into the female's oviduct. Spermatophores are capsules created by the males which contains sperm which is transferred during copulation. The hectocotylus can also be removed and given to the female to be stored in her mantle for as long as it takes for her eggs to be fertilized. The female octopus normally dies shortly after the fertilized eggs hatch, while the male normally dies two months after mating.
Periwinkle Snail
The Periwinkle Snail reproduces annually through an internal fertilization process. This means that the Periwinkle Snail is a hermaphrodite. The Periwinkle Snail is oviparous which means that it's eggs either have a very brief or no embryonic development. The Periwinkle Snail fertilizes it's eggs and then it sheds it's egg capsules in a mucus bundle into tide pools. The eggs are then washed out to sea and hatch after a larval development time of four to seven weeks.
Oyster
The Oyster reproduces through an external fertilization process, but can also reproduce through internal fertilization. This process involves the release of eggs by the female, while the male releases his sperm into the surrounding water. The two zygotes fuse together in the water and the eggs begin to develop. The oyster's gonads surrond the digestive organs and are made of branching tubules and sex cells. The Oysters glands release pheromones into the water. A pheromone is an excreted chemical that signals to males that the female is ready to reproduce.