Partula snails  (Partula spp)

These fascinating molluscs have captivated scientists for centuries, with an interesting reproductive strategy and a particularly impressive diversification of species. Occupying islands that were previously free of both competitors and predators, the Partula snails were able to fill every available niche, evolving many new species. In common with many other snail families, Partula snails are hermaphrodites, meaning that every individual produces both sperm and eggs, and possesses male and female reproductive organs. However, they do not self-fertilise, but instead court another individual by touching tentacles and lips. As they court, the male and female genitals begin to emerge from the skin behind the head, and the snails circle one another to position themselves for copulation. Before they copulate, these snails perform an extraordinary and unexplained behaviour. In a state of excitement, one of the snails expels a long, thin ‘love dart' made of chalk-like calcium carbonate, pushing it into its partner's head. Shortly afterwards, the other snail reciprocates, firing a return love dart – named as an analogy to Cupid's arrow. Copulation follows, and can last for up to eight hours, during which time the mating partners exchange spermatophores (4). Uniquely, both partners give birth to fully formed, shelled offspring two weeks after fertilisation (2).

Partula snails are thought to feed on algae and decaying plant matter and are known to live higher in trees as they mature. They are preyed upon by the introduced carnivorous snail, Euglandina rosea (2).