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Rotifera

(Phylum)

Overview

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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.

Taxonomy

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The Phylum Rotifera is a member of the Superphylum Gnathifera. Here is the complete "parentage" of Rotifera:

The Phylum Rotifera is further organized into finer groupings including:

Classes

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Bdelloidea

Bdelloidea () is a class of rotifers found in fresh water and moist soil. Bdelloids typically have a well-developed corona, divided into two parts, on a retractable head. They may move by swimming or crawling. The latter commonly involves taking alternate steps with the head and tail, as do certain leeches, which gives the group their name (Greek ?de??a or bdella, meaning leech). [more]

Eurotatoria

[more]

Monogononta

The monogononts (Monogononta) are a class of rotifers, found mostly in freshwater but also in soil and marine environments. They include both free-swimming and sessile forms. Monogononts generally have a reduced corona, and each individual has a single gonad, which gives the group its name. Males are generally smaller than females, and are produced only during certain times of the year, with females otherwise reproducing through parthenogenesis. [more]

Seisonidea

Seisonidae is a family of rotifers, found on the gills of Nebalia, a marine crustacean. Peculiar among rotifers, males and females are both present and equal in size. It is considered to have diverged from the other rotifers early on, and in one treatment is placed in a separate class Seisonoidea. [more]

At least 3 species and subspecies belong to the Class Seisonidea.

More info about the Class Seisonidea may be found here.

Sources

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Last Revised: October 03, 2013
2013/10/03 15:49:05