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Title: Rotifer  
Author: World Heritage Encyclopedia
Language: English
Subject: Asexual reproduction, Ctenophora, Acanthocephala, Gnathifera (clade), Gnathostomulid
Collection: Animal Phyla, Articles Containing Video Clips, Eocene First Appearances, Rotifers
Publisher: World Heritage Encyclopedia


Temporal range: Eocene–Recent
Rotaria sp.
Scientific classification
Kingdom: Animalia
(unranked): Protostomia
(unranked): Spiralia
(unranked): Platyzoa
Phylum: Rotifera
Cuvier, 1798
Classes and orders

The rotifers (Rotifera, commonly called wheel animals) make up a

  • Rotifer World Catalog, by Jersabek, C.D. & Leitner M.F.
  • Introduction to the Rotifera
  • Rotifers
  • Tree of Life Web Project
  • Rotifer Videos
  • Detailed description of Rotifers

External links

  1. ^ a b Harmer, Sidney Frederic and Shipley, Arthur Everett (1896). The Cambridge Natural History. The Macmillan company. p. 197. Retrieved 2008-07-25. 
  2. ^ Howey, Richard L. (1999). "Welcome to the Wonderfully Weird World of Rotifers". Micscape Magazine. Retrieved 19 February 2010. 
  3. ^ "Rotifers". FreshwaterLife. Retrieved 19 February 2010. 
  4. ^ Hendrik Segers (2007). Annotated checklist of the rotifers (Phylum Rotifera), with notes on nomenclature, taxonomy
  5. ^ Dec 2011 4th Internat. Barcode of Life conference, University of Adelaide
  6. ^ a b Bourne, A.G. (1907). Baynes, Spencer and W. Robertson Smith, ed. Encyclopaedia Britannica XXI (Ninth Edition ed.). Akron, Ohio: The Werner Company. p. 8. Retrieved 2008-07-27. 
  7. ^ Barnes, R.S.K.; Calow, P.; Olive, P.J.W.; Golding, D.W. & Spicer, J.I. (2001), The Invertebrates: a synthesis, Oxford; Malden, MA: Blackwell,  , p. 98
  8. ^ Baqai, Aisha; Guruswamy, Vivek; Liu, Janie; and Rizki, Gizem (2000-05-01). "Introduction to the Rotifera". University of California Museum of Paleontology. Retrieved 2008-07-27. 
  9. ^ Shimek, Ronald Ph.D (January 2006). "Nano-Animals, Part I: Rotifers". Retrieved 2008-07-27. 
  10. ^ Ruppert, Edward E.; Fox, Richard S, & Barnes, Robert D. (2004), Invertebrate zoology : a functional evolutionary approach (7th ed.), Belmont, CA: Thomson-Brooks/Cole,  , p. 788ff. – see particularly p. 804
  11. ^ Pechenik, Jan A. (2005). Biology of the invertebrates. Boston: McGraw-Hill, Higher Education. p. 178.  
  12. ^ a b c d e f g h i j k l Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 272–286.  
  13. ^ Jessica L. Mark Welch, David B. Mark Welch & Matthew Meselson (2004). "Cytogenic evidence for asexual evolution of bdelloid rotifers".  
  14. ^ "Photoreception."Encyclopædia Britannica from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD . 2009.
  15. ^ Claus-Peter Stelzer, Johanna Schmidt, Anneliese Wiedlroither & Simone Riss (2010). "Loss of sexual reproduction and dwarfing in a small metazoan".  
  16. ^ a b Hespeels B, Knapen M, Hanot-Mambres D, Heuskin AC, Pineux F, LUCAS S, Koszul R, Van Doninck K (July 2014). "Gateway to genetic exchange? DNA double-strand breaks in the bdelloid rotifer Adineta vaga submitted to desiccation". J. Evol. Biol. 27 (7): 1334–45.  
  17. ^ Wallace, R.L., T.W. Snell, C. Ricci & T. Nogrady (2006). Rotifera Vol. 1: Biology, ecology and systematics. Guides to the identification of the microinvertebrates of the continental waters of the world 23, 299 pp. Kenobi, Ghent/Backhuys, Leiden
  18. ^ Jersabek, C. D. & Leitner, M. F.2013: The Rotifer World Catalog. World Wide Web electronic publication. [1]
  19. ^ Jersabek, C. D. & Leitner, M. F.2013: The Rotifer World Catalog. World Wide Web electronic publication. [2]
  20. ^ Jersabek, C. D. & Leitner, M. F.2013: The Rotifer World Catalog. World Wide Web electronic publication. [3]

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Rotifers fall prey to many animals, such as copepods, fish (e.g. herring, salmon), bryozoa, comb jellies, jellyfish, and starfish.[17]


Bdelloid rotifer females cannot produce resting eggs, but many can survive prolonged periods of adverse conditions after brine shrimp, this desiccation tolerance is thought to be linked to the production of trehalose, a non-reducing disaccharide (sugar), bdelloids apparently cannot synthesise trehalose. In bdelloids, a major cause of the resistance to desiccation, as well as resistance to ionizing radiation, is a highly efficient mechanism for repairing the DNA double-strand breaks induced by these agents.[16] This repair mechanism likely involves mitotic recombination between homologous DNA regions. [16]


Males in the class Monogononta may be either present or absent depending on the species and environmental conditions. In the absence of males, reproduction is by parthenogenesis and results in offspring that are genetically identical to the parent. Individuals of some species form two distinct types of parthenogenetic eggs; one type develops into a normal parthenogenetic female, while the other occurs in response to a changed environment and develops into a degenerate male without a digestive system, but with a complete male reproductive system used to inseminate females thereby producing fertilized 'resting eggs' (also termed diapausing eggs). Resting eggs develop into zygotes that can survive extreme environmental conditions such as may happen during winter or when the pond dries up. These eggs resume development and produce a new female generation when conditions improve again.

Resting eggs

Recent transitions: Loss of sexual reproduction can be inherited in a simple Mendelian fashion in the monogonont rotifer Brachionus calyciflorus: This species can normally switch between sexual and asexual reproduction (cyclical parthenogenesis), but occasionally gives rise to purely asexual lineages (obligate parthenogens). These lineages are unable to reproduce sexually due to being homozygous for a recessive allele.[15]

‘Ancient asexuals’: Bdelloid rotifers are assumed to have reproduced without sex for many millions of years. Males are absent within the species, and females reproduce only by parthenogenesis.

Loss of sexual reproduction

The life span of monogonont females varies from two days to about three weeks.

Most species hatch as miniature versions of the adult. Sessile species, however, are born as free-swimming larvae, which closely resemble the adults of related free-swimming species. Females grow rapidly, reaching their adult size within a few days, while males typically do not grow in size at all.[12]

Fertilization is internal. The male either inserts his penis into the female's cloaca or uses it to penetrate her skin, injecting the sperm into the body cavity. The egg secretes a shell, and is attached either to the substratum, nearby plants, or the female's own body. A few species, such as Rotaria, are ovoviviparous, retaining the eggs inside their body until they hatch.[12]

Males do not usually have a functional digestive system, and are therefore short-lived, often being sexually fertile at birth. They have a single testicle and sperm duct, associated with a pair of glandular structures referred to as prostates (unrelated to the vertebrate prostate). The sperm duct opens into a gonopore at the posterior end of the animal, which is usually modified to form a penis. The gonopore is homologous to the cloaca of females, but in most species has no connection to the vestigial digestive system, which lacks an anus.[12]

The female reproductive system consists of one or two ovaries, each with a vitellarium gland that supplies the eggs with yolk. Together, each ovary and vitellarium form a single syncitial structure in the anterior part of the animal, opening through an oviduct into the cloaca.[12]

Rotifers are dioecious and reproduce sexually or parthenogenetically. They are sexually dimorphic, with the females always being larger than the males. In some species, this is relatively mild, but in others the female may be up to ten times the size of the male. In parthenogenetic species, males may be present only at certain times of the year, or absent altogether.[12]

Reproduction and life cycle

Rotifers eat particulate organic detritus, dead bacteria, algae, and protozoans. They eat particles up to 10 micrometres in size. Like crustaceans, rotifers contribute to nutrient recycling. For this reason, they are used in fish tanks to help clean the water, to prevent clouds of waste matter. Rotifers affect the species composition of algae in ecosystems through their choice in grazing. Rotifers may be in competition with cladocera and copepods for slowvagplanktonic food sources.

Video of a bdelloid rotifer feeding
Video of rotifer feeding, probably of the genus Cephalodella


Bdelloid rotifer genomes contain two or more divergent copies of each gene, suggesting a long-term asexual evolutionary history.[13] For example, four copies of hsp82 are found. Each is different and found on a different chromosome excluding the possibility of homozygous sexual reproduction. Its thin lamellae resemble cabbage leaves, and are composed from their creases of the receptor membrane.[14]

Like many other microscopic animals, adult rotifers frequently exhibit eutely—they have a fixed number of cells within a species, usually on the order of 1,000.

The coronal cilia pull the animal, when unattached, through the water.


Rotifers typically possess one or two pairs of short antennae and up to five eyes. The eyes are simple in structure, sometimes with just a single photoreceptor cell. In addition, the bristles of the corona are sensitive to touch, and there are also a pair of tiny sensory pits lined by cilia in the head region.[12]

Rotifers have a small brain, located just above the mastax, from which a number of nerves extend throughout the body. The number of nerves varies between species, although the nervous system usually has a simple layout. Close to the brain lies a retrocerebral organ, consisting of two glands either side of a medial sac. The sac drains into a duct that divides into two before opening through pores on the uppermost part of the head. Its function is unclear.[12]

Nervous system

A pair of osmotic balance.[12]

Behind the mastax lies an oesophagus, which opens into a stomach where most of the digestion and absorption occurs. The stomach opens into a short intestine that terminates in a cloaca on the posterior dorsal surface of the animal. Up to seven salivary glands are present in some species, emptying to the mouth in front of the oesophagus, while the stomach is associated with two gastric glands that produce digestive enzymes.[12]

The coronal cilia create a current that sweeps food into the mouth. The mouth opens into a characteristic chewing pharynx (called the mastax), sometimes via a ciliated tube, and sometimes directly. The pharynx has a powerful muscular wall and contains tiny, calcified, jaw-like structures called trophi, which are the only fossilizable parts of a rotifer. The shape of the trophi varies between different species, depending partly on the nature of their diet. In suspension feeders, the trophi are covered in grinding ridges, while in more actively carnivorous species, they may be shaped like forceps to help bite into prey. In some ectoparasitic rotifers, the mastax is adapted to grip onto the host, although, in others, the foot performs this function instead.[12]

Scanning electron micrographs showing morphological variation of bdelloid rotifers and their jaws.

Digestive system

The trunk forms the major part of the body, and encloses most of the internal organs. The foot projects from the rear of the trunk, and is usually much narrower, giving the appearance of a tail. The cuticle over the foot often forms rings, making it appear segmented, although the internal structure is uniform. Many rotifers can retract the foot partially or wholly into the trunk. The foot ends in from one to four toes, which, in sessile and crawling species, contain adhesive glands to attach the animal to the substratum. In many free-swimming species, the foot as a whole is reduced in size, and may even be absent.[12]

Modifications to the basic plan of the corona include alteration of the cilia into bristles or large tufts, and either expansion or loss of the ciliated band around the head. In genera such as Collotheca, the corona is modified to form a funnel surrounding the mouth. In many species, such as Testudinella, the cilia around the mouth have disappeared, leaving just two small circular bands on the head. In the bdelloids, this plan is further modified, with the upper band splitting into two rotating wheels, raised up on a pedestal projecting from the upper surface of the head.[12]

The most distinctive feature of rotifers is the presence of a ciliated structure, called the corona, on the head. In the more primitive species, this forms a simple ring of cilia around the mouth from which an additional band of cilia stretches over the back of the head. In the great majority of rotifers, however, this has evolved into a more complex structure.

Rotifers have bilateral symmetry and a variety of different shapes. The body of a rotifer is divided into a head, trunk, and foot, and is typically somewhat cylindrical. There is a well-developed cuticle, which may be thick and rigid, giving the animal a box-like shape, or flexible, giving the animal a worm-like shape; such rotifers are respectively called loricate and illoricate. Rigid cuticles are often composed of multiple plates, and may bear spines, ridges, or other ornamentation. Their cuticle is nonchitinous and is formed from sclerotized proteins.

Rotifer colonies
Colonial rotifers, tentatively identified as Conochilus from Lake Pontchartrain, Louisiana: the colony is somewhat less than 1 mm in diameter, but visible to the naked eye.
A colony of Sinantheria socialis on an Elodea densa leaf from North German Lake. Note heart-shaped corona of individuals.


The word "rotifer" is derived from a Latin word meaning "wheel-bearer",[11] due to the corona around the mouth that in concerted sequential motion resembles a wheel (though the organ does not actually rotate).


The Rotifera, strictly speaking, are confined to the Bdelloidea and the Monogonata. Rotifera, Acanthocephala and Seisonida make up a clade called Syndermata.[10]







The Acanthocephala, previously considered to be a separate phylum, have been demonstrated to be modified rotifers. The exact relationship to other members of the phylum has not yet been resolved.[9] One possibility is that the Acanthocephala are closer to the Bdelloidea and Monogononta than to the Seisonidea; the corresponding names and relationships are shown in the cladogram below.

About 2200 species of rotifers have been described. Their taxonomy is currently in a state of flux. One treatment places them in the phylum Rotifera, with three classes: Seisonidea, Bdelloidea and Monogononta.[7] The largest group is the Monogononta, with about 1500 species, followed by the Bdelloidea, with about 350 species. There are only two known genera with three species of Seisonidea.[8]

multicellular animals.[6]

Individual rotifers
A bdelloid rotifer

Taxonomy and naming


  • Taxonomy and naming 1
    • Etymology 1.1
  • Anatomy 2
    • Digestive system 2.1
    • Nervous system 2.2
    • Biology 2.3
  • Feeding 3
  • Reproduction and life cycle 4
    • Loss of sexual reproduction 4.1
    • Resting eggs 4.2
    • Anhydrobiosis 4.3
  • Predators 5
  • References 6
  • External links 7

In some recent treatments, rotifers are placed with acanthocephalans in a larger clade called Syndermata.

[5], among others, are actually species complexes.Lecane bulla, B. calyciflorus, Brachionus plicatilis evidence, however, suggests that some 'cosmopolitan' species, such as barcoding Recent [4].Lake Baikal to Cephalodella vittata species, like endemic, but there are also some cosmopolitan Most species of the rotifers are [3]

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