ANATOMY

THE BIVALVE MOLLUSK

Oysters are bivalve mollusks, meaning that they have flat bodies and a shell containing two hinged parts. These two shells are held tightly together when the oyster is shut by an adductor muscle that is attached to both the top and the bottom. An oyster has basic organs like a mouth, heart, stomach, anus, and reproductive glands, but no head. They lack a central nervous system, which we suspect means that they cannot feel pain. 

An oyster eats by pulling in water and processing it through cilia on their gills, which act like small filters that will consume the plankton transported through currents before they release the water back into the environment. Its mantle, the fleshy trim surrounding the oyster’s body, works to create the oyster’s shell over time. It also produces nacre, the illustrious mother of pearl that coats the interior part of the shell.  

An oyster absorbs more than just plankton when it eats. They can remove organic and inorganic toxins from the water like nitrogen and phosphorus by converting it into shell composite or expelling it as waste into material composites that don’t harm their ecosystem. The oyster’s filtration powers prevent things like algae blooms that eat up all the oxygen in water and kill off other wildlife.  

Photo cred: J‐P. Joly, Ifremer.

. . . THAT OYSTERS ARE HERMAPHRODITES?

Sequential hermaphrodites, that is! Oysters have the rare ability to change their sex! Almost all oysters are born male and remain that way for their first year of life. An oyster may then change sex based on its environmental surroundings or stress-induced situations. When waters warm and become ideal for spawning, an oyster will feel out its company and change to female based on the sex of the oysters close by. This helps provide an even balance of egg and sperm released into waters and optimizes the chances of procreation. There are a lot of ongoing studies on this!