Vertebrate or Invertebrate

The vertebrate category includes sea mammals, all of which must get their oxygen from above the water’s surface, and finfish, which obtain their oxygen from the water itself through their gills. Sea mammals include dolphin, whale, and seal, which are consumed in some cultures. Finfish are found in the fresh water of rivers, lakes, and streams, and the salt water of oceans and seas. The most popular finfish in North America are tuna, cod, Alaska pollack, salmon, catfish and flounder/sole.

Shellfish, which is a commercial rather than a scientific classification, includes the invertebrate crustaceans and mollusks. Examples of crustaceans are shrimp, crab, lobster, and crayfish. Mollusks include bivalves, univalves, and cephalopods. Bivalve creatures, including clams, oysters, mussels, and scallops, are contained within two hard shells that are hinged together. The univalves, such as conch and abalone, have only a single hard shell. Cephalopods, which include octopus and squid, have an almost rubbery soft inner shell, which will be familiar to parakeet owners as a cuttlebone.