Rotifer

Collotheca (genus)

Y. Tsukii

Rotifers are a group of microscopic animals that live just about anywhere there is fresh water, including lakes, ponds, streams, puddles, ditches, wet shorelines (especially sand), and even on wet mosses. On this page, we will focus on the Collotheca genus of rotifers.

Rotifers have a cylinder-shaped body made of three sections: head, trunk, and foot. The "foot" usually has two "toes" at the bottom. The head of a rotifer has a large, cup-shaped mouth, surrounded by cilia. Cilia are tiny hair-like things which wave back and forth. The rotifer's cilia are used to trap food and to move around through the water.

Some rotifer species spend most of their lives swimming around, but most Collotheca rotifers are sessile. "Sessile" means it attaches to one place and stays there for the rest of its life. The one time Collotheca swims is when it is young and hasn't found its place to attach yet. When the young rotifer is ready, it uses a sticky substance from its foot to attach itself to an aquatic plant. Greater Bladderwort is a favorite plant for Collotheca to attach to.

Micrographia

Microscopy-UK.org UK

Collotheca are large compared to most rotifers. Each rotifer has a clear tube it can pull itself into, like a turtle. The entire animal is transparent, so you can see its food inside.

To eat, Collotheca extends its body fully from its tube and waits for small swimming organisms to get close. Once an organism touches the rotifer's cilia, it gets sucked into its mouth. Common foods of rotifers include: algae, protozoa (such as amoeba and paramecium), small crustaceans (such as water fleas and copepods), and small bits of plant or animal matter floating in the current. They'll pretty much eat anything that fits into their mouths.

Nikon Microscopy U

The Chihuahuan Desert Springs Initiative

Collotheca reproduce by parthenogenesis. This means they don't have to mate, each rotifer can just make eggs by itself. When a Collotheca releases its eggs, they usually drift to the bottom. Eggs are very tough; they can last through the winter, and if the water level drops, they won't dry out.

When Collotheca hatch from their eggs, they are active swimmers, using their cilia to swim around in search of food and , eventually, a resting place.

Most rotifers live about a week. They are most plentiful in late Spring. Populations of rotifers can vary; one year a pond may have a great many, the next year almost none.

Predators of rotifers include aquatic insects, crustaceans (crayfish, water fleas, copepods), small fish, and amphibians.

Additional Media

Description
Type
Credit
Collotheca Rotifer Extending Its Body
Link to Video
Nikon Microscopy U
Collotheca Rotifer Eating Two Small Organisms
Link to Video
Nikon Microscopy U
Two Collotheca Rotifers Eating Algae (sped up)
Video
Cytographics
Collotheca Rotifer Moving and Eating
Link to Video
Olympus Digital Microscope

Relationships in Nature:

FOOD/PREY
PREDATORS
SHELTER
OTHER

Copepod

Copepod

Greater Bladderwort

Greater Bladderwort C

Water Flea

Water Flea

Yellow Pond Lily

Green Algae

Golden Shiner

Pickerelweed

Amoeba

Ebony Jewelwing

Marsh Bulrush

Euglena

Eastern Mosquitofish

Long-leaf Pondweed

Paramecium

Creek Chub

Hydrilla

Asian Tiger Mosquito

Greater Bladderwort

Common Duckweed

Eastern Newt

Common Cattail

Bluegill

Buttonbush

Bullfrog

Arrow Arum

Crayfish

Channel Catfish

American Toad

Three-lined Salamander

Yellow Perch

Wood Frog

Northern Caddis Fly

Euglena

Northern Hog Sucker

Eastern Lamp Mussel

Relationship to Humans:

Rotifers are an important part of any healthy body of fresh water, so by studying them, scientists can learn about the water they live in.

SCIENTIFIC CLASSIFICATION

KINGDOM
Animal
PHYLUM
Rotifera
CLASS
Monogononta
ORDER
Collothecacea
FAMILY
Collothecidae
GENUS
Collotheca
SPECIES
Collotheca (various species)

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