Aquatic Invertebrate Facts



Photo of a saddleback crayfish.
The saddleback crayfish occurs in the Big and Meramec river drainages, where it lives in clear, small to medium-sized creeks with rocky bottoms.
Chris Lukhaup

View aquatic invertebrates in the field guide.

Invertebrates are animals without a backbone, such as crayfish, clams, snails, leeches and insects. The bodies of many invertebrates, including crayfish and insects, are supported by external “skeletons” much like body armor. In order to grow, these “jointed-legged” animals (arthropods) must occasionally shed their exoskeletons as they develop larger new ones.

Snails and clams, however, increase the size of their calcium-enriched shells as they grow.

Leeches, planarians, hydras and other soft-bodied invertebrates have the ability to bend, expand and contract for different activities such as hunting, digesting, moving and hiding.

Aquatic invertebrates may live entirely beneath the water, or they may live upon its surface or on the plants surrounding it. Some breathe air, others breathe water. To move, they may walk, swim, float, skate, fly or glide on their bellies—or they may not move much at all.

Many insects lead double lives. Dragonflies, mayflies, stoneflies, caddis flies, dobsonflies and more are aquatic as juveniles. Then, when they undergo their final molt, they leave the water and become winged adults that fly in the air.

Other aquatic insects and spiders remain aquatic their whole lives. Water boatmen, predaceous diving beetles, whirligig beetles, water striders, fishing spiders and others spend all their days hunting in and around water. Some in this group can fly, however, and are attracted to lights at night.

Aquatic invertebrates are important in many ways

They are vital links in the aquatic food chain, conveying nutrients from plants and algae to larger organisms such as fish, frogs, salamanders, reptiles, birds and mammals.

Many fish depend on aquatic invertebrates for food. Some fish specialize in eating aquatic snails. Some eat mainly crayfish. Others prefer stoneflies, or mosquito larvae—and so on.

Hellgrammites, crayfish and others are popular bait for anglers. Many artificial lures resemble real-life invertebrates.

Invertebrates can tell us about water quality. Like the “canary in the coal mine,” they are sensitive to changes in sediment load, pollutants, pH and more. If their numbers decline, it could mean something’s going wrong that we need to pay attention to.

Some species—notably mosquitoes—are vectors for disease, with serious consequences for people. Many other aquatic invertebrates eat those species.

Harvesting freshwater mussels for button manufacture used to be a major industry in Missouri.

Crayfish are eaten by many people, and Missouri has recreational fisheries for them.

With their diversity of body forms and behaviors, aquatic invertebrates are simply fascinating. They are part of our rich natural heritage and deserve to be known better.

In This Section

Crayfish Facts

Colorful, quirky, and fascinating, Missouri's 35 species of crayfish (also called crawfish and crawdads) play a significant role in our state's diverse aquatic ecosystems, local economies, and heritage cuisines.

Freshwater Mussels Facts

If you love Missouri's clean water, thank our 65 species of freshwater mussels. As filter feeders, they clean impurities from the water.