According to Encyclopedia Britannica, the pelagic zone, or open ocean, includes animals classified as either zooplankton or nekton. Zooplankton are small organisms that drift in the ocean currents and make up an enormous portion of the ocean's food supply. Nekton are larger animals that swim independently of current.
Three phyla represent the pelagic zone's nekton. Chordate nekton include both bony and cartilaginous fish, marine reptiles and marine mammals. Cephalopods, such as the octopus and squid, are some of the molluscan nekton. Arthropods compose the final phylum of the pelagic zone's nekton, including crabs, lobsters and shrimp. Herbivorous nekton are uncommon, as most nekton live by consuming other animals.