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.


Water springtails congregate in water above soggy dead leaves
Water Springtails
Adult water springtails are bluish gray, often with reddish appendages. Their maximum length is about 1/8 inch.


Photo of a spotted fishing spider perched on the water's surface amid floating duckweed plants
Spotted Fishing Spider And Duckweeds
Both the spotted fishing spider and minute duckweed plants are able to float on the surface film of water.


Photo of backswimmer, side view
Backswimmer (Side View)
Backswimmers rest at the water surface tilted head-downward, with the abdomen tip protruding from the water. The oarlike hind legs are usually extended downward at angles to the body.


Photo of a fishfly larva crawling among rocks in an aquarium.
Fishfly Larva
Fishfly larvae look a lot like their cousins the hellgrammites, but they lack cottony or hairy gill tufts along the abdomen, and they have 2 short, fleshy tails at the hind tip.


Photo of an aquatic isopod in an aquarium, crawling on a rock.
Aquatic Isopod
Some freshwater isopods look a lot like the familiar land isopods that live under rocks in gardens.


Photo of amphipod on a rock
Amphipod (Scud) In Habitat


Photo of a gravid Mississippi grass shrimp in an aquarium.
Mississippi Grass Shrimp (Glass Shrimp; Ghost Shrimp)
Of Missouri’s two species of freshwater shrimp, the Mississippi grass shrimp is by far the most common and widespread.


Photo of a grassland crayfish, also called prairie crayfish.
Grassland Crayfish (Prairie Crayfish)
The grassland crayfish inhabits prairies and grasslands in northern and western Missouri.


Photo of a bristly cave crayfish, viewed from the side.
Bristly Cave Crayfish
The bristly cave crayfish lives in caves in the Springfield Plateau region of the Ozarks.






Photo of a ramshorn snail on a wet rock.
Ramshorn Snail
The shell of a ramshorn snail is a flat, disklike coil, similar to a ram's horn.


Photo of a leech
Many leeches have attractive speckled or striped patterns. A leech's head is usually at the more tapered (narrower) end.


Gray, speckled, translucent gelatinous blob cut in half to show structure
Bryozoan Colony Cut in Half
Bryozoan colonies of the species Pectinatella magnifica can form gelatinous masses as large as basketballs, although they are typically smaller.

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.