Animals without backbones that mostly live in oceans. Many can be found washed up on beaches. Examples: jellyfish, starfish, coral, sea urchins.

animals without skeletal structures that reside in the water such as insects, snails, crayfish, and amphipods.

Organisms that do not have a spinal column and live in water. Includes insects, crayfish, mites, etc.

any number of kinds of insects that have an exoskeleton (rather than a backbone) and live part of their lives in the water

Aquatic animals without an internal skeletal structure such as insects, mollusks, and crayfish.