Marine Invertebrates

Marine Invertebrates

Earliest Life Forms

Marine Invertebrates

Story Behind the Science

The population of marine invertebrates is extremely diverse, including animals like the octopus, crab, coral, jellyfish, sea star, clam, sponge, shrimp and so many more. These creatures are so fascinating because of their many differences from one another. For example, the octopus that captures its food with tentacles and suckers and eats with a beak-like mouth is much unlike a sponge that eats floating particles through a filtration feeding system.

There are approximately 230,000 marine species (both vertebrates and invertebrates) that have been described, however, the estimated number of undiscovered species in the oceans could be anywhere from several hundred thousand to perhaps even 10 million. Thousands of species of marine animals are discovered every year, and there are many more that have yet to be recognized or named.
Marine Invertebrates


Marine invertebrates play a crucial role in maintaining a stable and healthy marine ecosystem. Though they live in the oceans, they help to sustain life outside of the ocean as well, making them an important group of animals to protect. Since invertebrates make up around 97 percent of all living species in the world, they are very important in ensuring habitat quality, and they also act as the foundation for various food chains. Without these creatures, it is doubtful that humans would be able to survive.

Although marine invertebrates are not an especially threatened group, they are threatened due to the local and global pressures that affect the oceans they live in. Overfishing, habitat destruction, pollution and invasive species are a few of the issues marine invertebrates deal with as a result of human productivity. Climate change, though it shows evidence of being affected by humans, is also the result of natural phenomena like warming waters, variation in sea level, acidification, melting icecaps and changes in the ocean’s current systems.

Marine Invertebrates

Fast Facts

Did You Know?

  • Octopuses are masters of disguise and use multiple tactics to fight off predators. They can camouflage with their surroundings and release a black ink to distract predators and to momentarily dull their sense of smell. They can even lose an arm during an attack and re-grow it later.Learn More »
  • Sponges are classified as animals, not plants.Learn More »
  • Some marine invertebrates can change their sex at different stages of their lives. For example, some species of shrimp can begin life as a male and eventually become a female if necessary.Learn More »
  • The common octopus is considered the most intelligent of all invertebrates.Learn More »
  • Penguins, polar bears, sea lions and sea turtles are all marine vertebrates.Learn More »
Compare & Contrast Marine Invertebrates Marine Vertebrates
How many species? Approximately 170,000 accepted species Approximately 22,000 accepted species
Where do they occur? Marine invertebrates can be found in all oceans anywhere from the sea surface to its floor, even in extreme hot or cold temperatures. Like marine invertebrates, these animals can be found worldwide and in extreme temperatures. Some marine reptiles, mammals and birds can even live on land.
What do they eat? Some marine invertebrates eat zooplankton, phytoplankton or algae. Others may eat fish, crabs, shellfish, barnacles or the dead, decaying bodies of other animals. Other marine animals act as the food source for marine vertebrates. Fish, seals, sea turtles, shellfish and other marine invertebrates are a few examples. Though some marine vertebrates live mainly on land, they depend greatly on other marine animals as a food source.
Do they have predators? Other marine invertebrates and vertebrates. For example, a shark may prey on an octopus, which may prey on a crab or a sponge. Predators of marine vertebrates generally include other marine animals like fish, octopuses, whales, dolphins, birds and many more.

National Geographic, "Great Migrations: Jellyfish in Danger"

Marine Invertebrates