Flatworm

Procotyla fluviatilis

Copyright, Mark Cooper, Mt. San Antonio College

Flatworms, also called "planarians," are found just about everywhere there is water. There are many different species of flatworms, but this page will focus on Procotyla fluviatilis, one of our more common ones.

It is difficult to find pictures of Procotyla fluviatilis, so the images on this page are not necessarily that species. Most flatworms look very similar, though, so Procotyla fluviatilis looks a lot like these pictures.

One of the reasons Procotyla fluviatilis is so common is because it is able to live in most bodies of water, including streams, ponds, and lakes. Like most flatworms, they prefer shallow water.

Electronic Field Guide to Aquatic Invertebrates of Small Streams in Eastern Massachusetts

Procotyla fluviatilis grows up to 20 millimeters long. They are usually brown or greenish.

All flatworms have a soft body and a triangle-shaped head. They also have eye-spots on top of their heads which can see light. Flatworms are not closely related to most other "worms," such as earthworms. Bodies are flat instead of round, and they do not have segments.

Flatworms spend most of their time on the bottom, especially since they can't swim. They release sticky mucus (a lot like slugs and snails) which they glide on top of. They can crawl up plants, and they can glide upside down on the surface of the water.

Flatworms do not like light. They stay in the shade or under rocks or other items during the day.

There are no male or female flatworms. They are hermaphrodites, which means when they mate, both flatworms can lay eggs. Several eggs are laid in one cocoon two to four millimeters wide. Eggs hatch in about two weeks, unless it's near Winter. Then the eggs wait until Spring.

Young Procotyla fluviatilis are 1 to 3 millimeters long when they hatch.

Most flatworms, including Procotyla fluviatilis, are predators. They eat protists (including Amoeba, Paramecium, and Euglena), rotifers, nematodes, small crustaceans, aquatic worms, and other soft-bodied animals. They also feed on dead animal matter and larger animals that are injured. Sometimes they even eat other flatworms, including their own kind! A flatworm is able to stretch part of its mouth and use it to suck the juices of its prey.

Procotyla fluviatilis can also release some mucus as a trap to catch small crustaceans.

Cabot School

Dr. Rick Gillis, http://www.uwlax.edu/biology/faculty/Gillis/gillis.htm

Flatworms have many predators, including aquatic insects, such as dragonfly naiads and diving beetles. Tadpoles, small fish, and crustaceans also eat them.

Sometimes flatwoms, such as Procotyla fluviatilis, are transported by larger animals to new places. When a bird, raccoon, or other animal gets mud on its feet, flatworms inside the mud get a free ride. Of course, if the larger animal doesn't go somewhere there is water, and the flatworm dries out, it dies.

Procotyla fluviatilis can also migrate by streams to other bodies of water.

Flatworms are less active when the water is very warm or when they are fully fed.

Relationships in Nature:

PREY/FOOD
PREDATORS
SHELTER
OTHER

Amoeba

Copepod

Yellow Pond Lily

Great Blue Heron C

Euglena

Water Flea

Lizard's Tail

Canada Goose C

Paramecium

Water Mite

Pickerelweed

Mallard C

Rotifer

Green Darner

Long-leaf Pondweed

Wood Duck C

Brainworm Nematode

Ebony Jewelwing

Common Duckweed

Predatory Nematode

Crayfish

Arrow Arum

Flatworm

Large Diving Beetle

Common Cattail

Aquatic Worm

Eastern Dobsonfly

Common Reed

Copepod

Predatory Nematode

Buttonbush

Scud

Flatworm

Hydrilla

Water Flea

Asian Tiger Mosquito

Crane Fly

Northern Caddis Fly

Green Hydra

Relationship to Humans:

Procotyla fluviatilis, and other flatworms, are important parts of healthy streams, ponds, and lakes. They need clean water with lots of oxygen, so when we don't find them, that tells us the water is not healthy. They also provide food for animals, like dragonflies, when they are young. Dragonflies later help us control pests (like mosquitoes) when they are adults.

SCIENTIFIC CLASSIFICATION

KINGDOM
Animal
PHYLUM
Platyhelminthes
CLASS
Turbellaria
ORDER
Tricladida
FAMILY
Dendrocoelidae
GENUS
Procotyla
SPECIES
Procotyla fluviatilis

QUICK LINKS

Organism Menu
Home
Glossary
Student Activities
Relationships
Classification Info
How to Use This Site
Bibliography