Rotifera(redirected from rotifer)
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Rotifera,phylum of predominantly free-living, microscopic, aquatic or semiterrestrial pseudocoelomatespseudocoelomate
, any of a group of invertebrates with a three-layered body that has a fluid-filled body cavity (pseudocoelom) between the endoderm and the mesoderm (the innermost and middle tissue layers).
..... Click the link for more information. . Each rotifer has a head bearing a crown of cilia, the corona, at the anterior end; most rotifers feed with the aid of currents generated by the coronal cilia. A posterior foot, often equipped with two or three toes, contains adhesive glands permitting temporary attachment to objects. Unique grinding jaws are found in the pharynx, and an esophagus, stomach, and intestine can be distinguished. The excretory system consists of ciliated cells, called flame cells, that move collected liquids into two coiled tubes called protonephridia; these tubes open into a contractile bladder. The reproductive system is simple, consisting in the female of ovary, yolk gland, and oviduct, and in the male of testis and sperm duct. The intestine, bladder, and reproductive ducts unite to form a cloaca.
Rotifers, of which there are about 1,500 known species, are widely distributed in freshwater and marine habitats; they also live in the soil, in mosses, and associated with lichens on rocks and trees. A few are parasitic. Most feed on bacteria, algal cells, small protozoans, or organic detritus. As a rule, only female rotifers are seen; in some species the males have never been observed. Diploid eggs develop parthenogenetically, i.e., without fertilization, to produce females. Under some conditions, haploid eggs are produced; these develop parthenogenetically into males or can be fertilized, developing into dormant female embryos with heavy shells (resting eggs). Many species can survive in a dry form for long periods of time, emerging from a dormant state and becoming active when moisture is available.
A phylum of pseudocoelomate, microscopic, mainly free-living aquatic animals, characterized by an anterior ciliary apparatus, the corona, whose cilia when in motion have the appearance of a pair of rapidly rotating wheels. This structure is implicit in the phyletic name (literally “wheel bearers”) and the older popular name wheel animalcules.
The Rotifera show considerable diversity in form and structure, but all are bilaterally symmetrical, pseudocoelomate animals possessing complete digestive, excretory, nervous, and reproductive systems, but lacking separate respiratory and circulatory systems. They possess two features unique to their phylum: the corona, which is a retractile trochal disk, and the mastax, which is a gizzardlike structure derived from the modified pharynx.
Rotifers are dioecious and sexually dimorphic; females are commoner than males, some of which are degenerate organisms lacking a mouth and digestive organs. Males, when produced in the life cycle, are short-lived and survive for only hours or at the most a few days.
The three major subdivisions of the Rotifera, now given class status, are the Seisonacea, Bdelloidea, and Monogononta.