At the Rotifer Club

What am I looking at?

This is an image of six different rotifers surrounding a single desmid (a microscopic alga) in the center. The rotifers’ chitinous exoskeletons (1) are blue, and their cilia, which are used for movement and feeding, are red (2). The desmid’s cell wall is blue as well; the red structures in the center of the desmid (3) are its two large chloroplasts.

Biology in the background

Rotifers, known as “wheel animals,” live all over the globe and are part of the nutrient-recycling process of many underwater ecosystems. They eat small organic particles like bits of plants, bacteria, and other microscopic organisms. In turn, they are fodder for fish and insect larvae.

The cilia that allow them to swim are located mainly around their mouth and can also be used to sweep food particles into their muscular pharynx, called a mastax (notice that each of the rotifers also has two tiny tufts of cilia located toward the rear of its body; these are used for steering). In this way, they “clean” the water they live in, keeping it from getting too packed with a single type of microorganism, such as algae, or from filling up with dead plant matter. They are so good at this that some fish owners and even aquarium staff use rotifers to help clean the water in tanks containing fish and other aquatic animals.

Rotifers vary in size quite a bit, ranging from 50 micrometers, or slightly smaller than the width of a human hair, to over 2 millimeters, or roughly 10 times smaller than the width of a human thumbnail.

Technique

These images were created using confocal microscopy.