Fornicating Slipper Snail - Crepidula fornicata
Common slipper shells start their lives as males, but some change to females as they grow older. The change is initiated by a waterborne hormone that regulates the female characteristics. Once they change into females, they remain females. To make reproduction more convenient, they often stack up on top of each other with the larger females on the bottom, the smaller males on top, and the hermaphrodites in the middle. If the ratio of males to females gets too high, the male reproductive organs will degenerate and the animal will become female.
Habitat: Washed up on the beach during low tide. It had red seaweed attached to it, but I didn't get a close enough look to ID it.
The common slipper shell is a species of medium-sized sea snail, a marine gastropod mollusc in the family Calyptraeidae, the slipper snails and cup and saucer snails.
