Using tongs or a similar apparatus, put the identifying species in a confined aquarium or tank for easy observation. Put on any necessary observation tools like reading glasses or use a magnifying glass to help observe the animal.
Examine the outside of the animal's body. If it is a crustacean, it will have a segmented body with an exoskeleton. An exoskeleton is a hard outside shell that encases the insides. Segments are separated compartments of the body such as an abodomen, head or posterior.
Examine the limbs of the animal. They should be branched, meaning that they will have several sections. Look for these branches on the legs.
Look at the top of the animal's head and see if there are any antennae. Crustaceans typically have two pairs of antennae.
Count the legs on the animal to see if it has multiple pairs of legs. Crustaceans have multiple pairs of appendages on their body for easy movement, feeding and sexual reproduction.
Fill the tank with enough water so that the animal is submerged. Crustaceans have gills for respiration and should be able to survive and swim in an aqueous environment.