Rotifers: Rotifera

Most rotifers collect food by beating the wheel organ to make a water current. Swimming rotifers move gently through the water in a spiral motion. Crawling rotifers use sticky glands on their foot and head to move much the way inchworms do.

Some species of rotifers use only sexual reproduction; some use only asexual reproduction, and others have both a sexual and an asexual phase. Asexual (ay-SEK-shuh-wuhl) means without and sexual means with the uniting of egg and sperm for the transfer of DNA from two parents. In species that use only asexual reproduction, all the rotifers are females. The female produces eggs that develop into new embryos without fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development. The daughters are genetically identical to the mother.

In rotifers that use only sexual reproduction the males store sperm in a bag that they transfer to females during mating. Fertilization takes place inside the females. Later the females attach the eggs to crustaceans called sea fleas, where they stay until the young hatch. Crustaceans (krus-TAY-shuns) are water-dwelling animals that have jointed legs and a hard shell but no backbone.

Among rotifers that have two reproductive phases, the asexual phase has only females that produce more females without fertilization. Certain physical events, however, can produce sexually reproducing females, whose eggs can be fertilized (FUR-teh-lyzed) by a male. If not fertilized, the eggs develop into dwarf males. These males do not live long and immediately after hatching seek a female and fertilize her eggs by injecting her with sperm. The thick-shelled egg that results can survive extreme conditions such as freezing and drying out. After a resting period, an asexually reproducing female hatches from the egg.