Gills are specialized structures in shellfish that facilitate the exchange of oxygen and carbon dioxide between the water and the bloodstream, enabling them to breathe underwater.

Gills in shellfish not only serve as respiratory organs but also play a crucial role in filter feeding. They trap food particles suspended in the water, allowing the shellfish to extract nutrients.

The adductor muscle is a powerful muscle that runs through the center of the bivalve shell, connecting the two halves. It is responsible for opening and closing the shell.

The mantle is a thin layer of tissue that lines the inside of the shell. It secretes calcium carbonate, which hardens and forms the protective outer shell.

Siphons are tube-like structures found in some shellfish. They serve dual purposes: one siphon is used for taking in water for respiration and filter feeding, while the other expels waste products.

Gastropods are a class of shellfish characterized by their single, spiral-shaped shell. Examples include snails, limpets, and abalone.

The byssus is a specialized foot found in some shellfish, such as mussels and barnacles. It consists of strong threads that the shellfish uses to attach itself to rocks or other surfaces.

Sensory tentacles are specialized structures found in some shellfish, such as clams and scallops. They are used to detect changes in the environment, including the presence of predators.

The gonad is the reproductive organ in shellfish. It produces eggs (ova) in females and sperm in males.

Bivalves are a class of shellfish characterized by their hard outer shell, which consists of two hinged valves. Examples include clams, oysters, and mussels.

The kidney is the excretory organ in shellfish. It filters waste products from the bloodstream and expels them from the body.

Cephalopods are a class of shellfish characterized by their soft bodies and a pair of muscular fins for locomotion. Examples include squid, octopus, and cuttlefish.

The foot in some shellfish is modified into a specialized structure that allows them to burrow into the sand or mud. This adaptation is commonly found in clams and cockles.

Crustaceans are a class of shellfish characterized by their segmented bodies and jointed appendages, such as claws and legs. Examples include crabs, lobsters, and shrimp.

The statocyst is a sensory organ found in some shellfish, such as scallops and abalone. It helps them maintain their balance and orientation in the water by detecting changes in gravity and acceleration.