Self-Taught Lesson #9: Does octopus count as a shellfish?

What defines a shellfish?

Shellfish is consists of two groups, crustaceans and mollusks.

A crustacean is an animal with an exoskeleton and the ability to traverse and live on land and underwater. They have legs, sometimes claws. Think of crabs, lobsters, crawfish, and shrimp.

A mollusk is an underwater-living organism with a hard, exterior shell and a soft pulp of meat inside. It pumps water in and out of its shell. Mollusks with two even shells that hinge together like a compact mirror, like cl...