Rotifera

Rotifera phylum of predominantly free-living, microscopic, aquatic or semiterrestrial pseudocoelomates . 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.

Rotifera A phylum of microscopic (0.04–2.00 mm) pseudocoelomate aquatic animals characterized by a crown of cilia at the head end. These are used in locomotion and in some species for feeding: the crown resembles a rotating wheel when the cilia are beating. Rotifers possess jaws and are covered with a layer of chitin (the lorica). There is no circulatory system and gas exchange occurs across the body surface. Some rotifers reproduce by parthenogenesis.

Rotifera (Rotatoria; wheel animalcules; phylum Aschelminthes) A class (or phylum in some classifications) of acoelomate, unsegmented animals in which normally a complete alimentary canal is present, as is a muscular pharynx possessing well-developed jaws. Their name is derived from the ciliated crown which in many species gives the appearance of a rotating wheel when it beats. The largest individuals reach 3 mm in length, but most are much smaller. Most are solitary and free-moving, but some are sessile and some colonial. They occur mainly in freshwater habitats. They swim by means of their cilia, or crawl across a substrate by muscular movements. Most are benthic. The body is always covered by a cuticle, which may be ornamented. There is a pseudocoelom between the body wall and gut. Some feed on suspended matter, others are predatory on protozoa, rotifers, or small metazoan animals. Most are non-parasitic. All (except Bdelloida) reproduce sexually. There are about 1800 species, grouped in two classes: Digononta, comprising the orders Seisonidea and Bdelloida, and containing rotifers with two ovaries; and Monogonta, with one ovary, comprising the orders Flosculariacea, Collothecacea, and Ploima.