Nematodes [Aschelminthes]

These animals are very small. They are part of the meiofauna, those organisms living between the grains of sediments. These are most abundant near surface sediments, where food and oxygen are more abundant. Nematodes feed on bacteria and protozoa. They serve as food for deposit feeders like worms and amphipods, providing a link in the food web between the unicellular organisms and these larger animals.

Nematoda
These transparent, thread-like worms are tapered at both ends and are minute, typically about one-quarter inch long. They squirm from side to side or spiral in the sediments, serving to circulate and aerate them.

There are 80,000 known species, and estimates of the number of kinds on the planet range from a half to one million. Considering all the individuals of each species, scientists figure these are the most numerous invertebrates on the planet.

Rotifers
These worm-like animals, also minute, consume unicellular food particles. They draw them into their mouths by creating water current with circles of hair-like appendages called cilia. The beating cilia create the illusion of a spinning wheel, giving the creatures their name. The microbes are ground by jaws behind their mouths, before being further broken down by enzymes.

Copyright © 2006 Barbara Driscoll.