Salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Edible raw or cooked.

When they are spawning, they are stuffed with both eggs and sperm. A female can produce half a billion eggs a year and a male three billion sperm.

Oysters usually spend their first spawning season as males and then change radically, he said. Testes become ovaries and for the rest of their life they are egg-making machines. The smaller oysters are usually male and the larger ones female, he said.

Of the multitude of eggs produced, some are fertilized. “But most will become part of the planktonic soup which feeds so many creatures.