There are more than twice as many species of crustaceans than the combined number of species of all mammals, reptiles, amphibians, and birds. Crabs, crawfish, pill bugs, barnacles, lobsters, and water fleas are all crustaceans.

Crustaceans have no internal skeleton and rely on their hard calcium exoskeleton for structure. Swimming legs, known as swimmerets, hold the eggs for females, while the first pair of swimmerets on the males’ abdomens is enlarged and serves to pass sperm to the females.

In 2013, the discovery of the first venomous crustacean was announced. Of the over 70,000 species, the blind, underwater-cave-dwelling “remipede” is the first known venomous crustacean.