Bdelloidea

(invertebrate zoology) An order of the class Rotifera comprising animals which resemble leeches in body shape and manner of locomotion.

A class (formerly order) of the phylum Rotifera. Bdelloid rotifers have a very characteristic appearance; the agile elongate body consists of several (typically 16) false segments or annuli which do not correspond to the true segmentation of the body. Of these, the shorter and smaller head, neck, and foot segments are telescopically retractile into the larger and longer trunk joints. In typical species the corona has the characteristic form of two trochal disks, raised on pedicels, and a single cingulum of smaller cilia. The corona can be completely withdrawn, to reveal the true anterior end of the body. The mouth is large and funnel-shaped, and leads via a ciliated buccal tube into the mastax (a gizzardlike structure) whose ramate trophi are in constant motion. The intestine is syncytial, often colored brown or red by its contents, and digestion appears to be extracellular, rapid, and occurring in an alkaline medium. No males are known, and reproduction is believed to be parthenogenetic. A few genera are viviparous, but most are oviparous.

The Bdelloidea are typically bottom dwellers and crawl over the substratum leech-fashion. They are the most common inhabitants of standing fresh waters throughout the world, occurring in the smallest pools, in the littoral zones of large lakes, and also in mosses, liverworts, and lichens, some of which may be wetted only intermittently. See also Rotifera.