Animals That Live in the Ocean

Did you know there are over 250,000 species of animals living in the world's oceans? Scientists are discovering constantly discovering new animal species thanks to new underwater vehicles, but the vast majority of the oceans have not been fully explored!

Types of Ocean Animals

Ocean Fish Facts

• Ocean fish live in salt water during their entire life, although there are some exceptions. One exception is the rainbow trout, which is born in freshwater. Some rainbow trout travel to saltwater and live in the ocean. When they move to saltwater, they physically change and then are known as Steelhead. Steelhead return to freshwater to spawn, then the cycle starts over again. If the rainbow trout do not travel to the ocean, they remain rainbow trout.


• Fish that live in the ocean breathe by using their gills, similar to freshwater fish, to extract oxygen from the water.


• Most fish are cold-blooded, but two types of fish, the tuna family, mackerel and some sharks, are warm blooded or have a body temperature that changes independent of the surround water.


• Scientists have identified more than 28,000 types of fish. Since these are many unexplored areas of water, scientists believe there are many more types of fish.

Invertebrate Facts

Invertebrates represent the largest number of animals in the ocean. There are 17 main groups of invertebrate identified by scientists which live in the sea.

• There are five major groups, known as phylum, of invertebrate found in the ocean, including Cnidarians, Arthropods, Mollusca, Annelida and Echinoderms. There are many more classes of invertebrate below the major phylum. Some of these classes include Crustaceans, Sipuncula, Echiura, Nematoda, Nemertea, Platyhelminthes, Ctenophara, Hermichordata, Chaetognatha, Brachiopoda, Bryozoa, Phoronida, and Sponges.


• Over 75 percent of the known animal species are Invertebrates.


• Scientists think there could be millions of unknown ocean invertebrate species that have not been identified.


• Arthropods, which includes the largest number of animals on Earth (over 1 million types), are a diverse group of animals which include insects. Ocean arthropods include crabs, prawns, horseshoe crabs and lobster. Arthropods are known for having an exoskeleton which is a hard protective outer surface on their body.


• Cnidarians include a wide range of ocean animals. coral is a cnidarian. When this tiny creature dies its body becomes part of a large rock-like substance in the ocean. Jellyfish and sea anemone are also included in this group of invertebrates.


• The mollusca group includes oysters, mussels, clams, squid, octopus, scallops, snails, slugs and many more species.


• The sponge group includes natural sponges, which were used for years by people. Many sponges are found near coral reefs.


• The echinoderm group have have a exoskeleton to protect their body. Sea cucumbers, sea urchins and star fish are all types of echinoderm.


• Sipuncula, Echiura, Nematoda, Nemertea, Platyhelminthes, Phoronida, Hemichordata, Chaetognatha and Ctenophara are all types of sea worms.