What Lives in the Ocean?

The ocean is home to many different species of plankton, marine invertebrates, cephalopods, marine mammals and sea turtles. Other creatures that live in the ocean include numerous types of fish, sharks and corals.

There are two main types of plankton: phytoplankton, which are plant based, and zooplankton, which are animal based. Phytoplankton are also broken down into large and small species. The large species consist of diatoms and dinoflagellates, while the small species consist of nanoplankton and picoplankton.

Zooplankton are classified by their size as well as their stage of development. Their size categories include picoplankton, nanoplankton, microplankton, mesoplankton, macroplankton and megaplankton. The stages of development of zooplankton are meroplankton and holoplankton. Meroplankton are larvae that turn into worms, mollusks, crustaceans or coral. They also change into echinoderms, fish or insects. Holoplankton do not change form and instead remain plankton for their entire lifespan. Types of holoplankton include pteropods, chaetognaths, larvaceans, siphonophores and copepods.

Marine invertebrates are marine animals that do not have backbones, including sponges, worms, molluscs, anthropods and echinoderms. Cephalopods include species of octopus and squid, such as the Australian giant cuttlefish, the Caribbean reef octopus and the vampire squid. Some marine mammals that live in the sea include dolphins, such as the bottlenose dolphin and the long-snouted spinner dolphin, and whales, such as the bowhead whale and the humpback whale.