The Info List - Rotifer

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The rotifers (Rotifera, commonly called wheel animals) make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Antonie van Leeuwenhoek
Antonie van Leeuwenhoek
in 1703.[1] Most rotifers are around 0.1–0.5 mm long (although their size can range from 50 μm to over 2 mm),[2] and are common in freshwater environments throughout the world with a few saltwater species; for example, those of genus Synchaeta. Some rotifers are free swimming and truly planktonic, others move by inchworming along a substrate, and some are sessile, living inside tubes or gelatinous holdfasts that are attached to a substrate. About 25 species are colonial (e.g., Sinantherina semibullata), either sessile or planktonic. Rotifers are an important part of the freshwater zooplankton, being a major foodsource and with many species also contributing to the decomposition of soil organic matter.[3] Most species of the rotifers are cosmopolitan, but there are also some endemic species, like Cephalodella vittata to Lake Baikal.[4] Recent barcoding evidence, however, suggests that some 'cosmopolitan' species, such as Brachionus
plicatilis, B. calyciflorus, Lecane bulla, among others, are actually species complexes.[5][6] In some recent treatments, rotifers are placed with acanthocephalans in a larger clade called Syndermata.


1 Taxonomy and naming

1.1 Etymology

2 Anatomy

2.1 Digestive system 2.2 Nervous system 2.3 Biology

3 Feeding 4 Reproduction and life cycle

4.1 Loss of sexual reproduction system 4.2 Resting eggs 4.3 Anhydrobiosis

5 Predators 6 Genome size 7 Gallery 8 References 9 External links

Taxonomy and naming[edit] See also: List of bilaterial animal orders

Individual rotifers

A bdelloid rotifer

Ptygura pilula


Rev. John Harris first described the rotifers (in particular a bdelloid rotifer) in 1696 as "an animal like a large maggot which could contract itself into a spherical figure and then stretch itself out again; the end of its tail appeared with a forceps like that of an earwig".[1] In 1702, Anton van Leeuwenhoek
Anton van Leeuwenhoek
gave a detailed description of Rotifer
vulgaris and subsequently described Melicerta ringens and other species.[7] He was also the first to publish observations of the revivification of certain species after drying. Other forms were described by other observers, but it wasn't until the publication of Christian Gottfried Ehrenberg's Die Infusionsthierchen als vollkommene Organismen in 1838 that the rotifers were recognized as being multicellular animals.[7] 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.[8] 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.[9] 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.[10] 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.







The Rotifera, strictly speaking, are confined to the Bdelloidea
and the Monogononta. Rotifera, Acanthocephala
and Seisonida make up a clade called Syndermata.[11] Etymology[edit] The word "rotifer" is derived from a Latin word meaning "wheel-bearer",[12] due to the corona around the mouth that in concerted sequential motion resembles a wheel (though the organ does not actually rotate). Anatomy[edit]


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
Elodea densa
leaf from North German Lake. Note heart-shaped corona of individuals.

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. 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. 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.[13] 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.[13] Digestive system[edit]

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

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.[13] 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.[13] A pair of protonephridia open into a bladder that drains into the cloaca. These organs expel water from the body, helping to maintain osmotic balance.[13] Nervous system[edit] 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. The function of the retrocerebral organ is unclear.[13][14] The nervous system comprises about 25% of the roughly 1,000 cells in a rotifer.[14] 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.[13] Biology[edit] The coronal cilia pull the animal, when unattached, through the water. 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. Bdelloid
rotifer genomes contain two or more divergent copies of each gene, suggesting a long-term asexual evolutionary history.[15] For example, four copies of hsp82 are found. Each is different and found on a different chromosome excluding the possibility of homozygous sexual reproduction. Feeding[edit]

Play media

Video of rotifer feeding, probably of the genus Cephalodella

Play media

Video of a bdelloid rotifer feeding

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 planktonic food sources. Reproduction and life cycle[edit] 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.[13] 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.[13] 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.[13] The phylum Rotifera
encloses three classes that reproduce by three different mechanisms: Seisonidea reproduce exclusively bisexually; Bdelloidea
reproduce exclusively by asexual parthenogenesis; Monogononta
reproduce alternating these two mechanisms (“cyclical parthenogenesis” or “heterogony”).[16] Parthenogenesis
(amictic phase) dominates the monogonont life cycle, promoting fast population growth and colonization. In this phase males are absent and amictic females produce diploid eggs by mitosis which develop parthenogenetically into females that are clones of their mothers.[16] Some amictic females can generate mictic females that will produce haploid eggs by meiosis. Mixis (meiosis) is induced by different types of stimulus depending on species. Haploid eggs develop into haploid dwarf males if they are not fertilized and into diploid “resting eggs” (or “diapausing eggs”) if they are fertilized by males. 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.[13] 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.[13] The life span of monogonont females varies from two days to about three weeks. Loss of sexual reproduction system[edit] ‘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. 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.[17] Resting eggs[edit] Resting eggs enclose an embryo encysted in a three layered shell that protects it from external stressors.[18][19] They are able to remain dormant for several decades and can resist adverse periods (e.g., pond desiccation or presence of antagonists).[20][21] When favourable conditions return and after an obligatory period of diapause which varies among species, resting eggs hatch releasing diploid amictic females that enter into the asexual phase of the life cycle.[16][22] Anhydrobiosis[edit] Bdelloid
rotifer females cannot produce resting eggs, but many can survive prolonged periods of adverse conditions after desiccation. This facility is termed anhydrobiosis, and organisms with these capabilities are termed anhydrobionts. Under drought conditions, bdelloid rotifers contract into an inert form and lose almost all body water; when rehydrated they resume activity within a few hours. Bdelloids can survive the dry state for long periods, with the longest well-documented dormancy being nine years. While in other anhydrobionts, such as the 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.[23] This repair mechanism likely involves mitotic recombination between homologous DNA regions.[23] Predators[edit] Rotifers fall prey to many animals, such as copepods, fish (e.g. herring, salmon), bryozoa, comb jellies, jellyfish, starfish, and tardigrade.[24] Genome size[edit] The genome size of a bdelloid rotifer, Adineta vaga, was reported to be around 244 Mb.[25] The genomes of Monogononts seem to be significantly smaller than those of Bdelloids. In Monogononta
the nuclear DNA content (2C) in eight different species of four different genera ranged almost fourfold, from 0.12 to 0.46 pg.[26] Haploid "1C" genome sizes in Brachionus
species range at least from 0.056 to 0.416 pg.[27] Gallery[edit]

Pair of Lepadella Rotifers, from pond water in Northeast US.


^ a b Harmer, Sidney Frederic & Shipley, Arthur Everett (1896). The Cambridge Natural History. The Macmillan company. p. 197. Retrieved 2008-07-25.  ^ Howey, Richard L. (1999). "Welcome to the Wonderfully Weird World of Rotifers". Micscape Magazine. Retrieved 2010-02-19.  ^ "Rotifers". FreshwaterLife. Retrieved 2010-02-19.  ^ Hendrik Segers (2007). Annotated checklist of the rotifers (Phylum Rotifera), with notes on nomenclature, taxonomy ^ Gómez, Africa; Serra, Manuel; Carvalho, Gary R.; Lunt, David H. (July 2002). "Speciation in ancient cryptic species complexes: evidence from the molecular phylogeny of Brachionus
plicatilis (Rotifera)". Evolution; International Journal of Organic Evolution. 56 (7): 1431–1444. doi:10.1111/j.0014-3820.2002.tb01455.x. ISSN 0014-3820. PMID 12206243.  ^ Dec 2011 4th Internat. Barcode of Life conference, University of Adelaide ^ a b Bourne, A.G. (1907). Baynes, Spencer and W. Robertson Smith, ed. Encyclopædia Britannica. XXI (Ninth ed.). Akron, Ohio: The Werner Company. p. 8. Retrieved 2008-07-27.  ^ 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, ISBN 978-0-632-04761-1 , p. 98 ^ Baqai, Aisha; Guruswamy, Vivek; Liu, Janie & Rizki, Gizem (1 May 2000). "Introduction to the Rotifera". University of California Museum of Paleontology. Retrieved 2008-07-27.  ^ Shimek, Ronald (January 2006). "Nano-Animals, Part I: Rotifers". Reefkeeping.com. Retrieved 2008-07-27.  ^ Ruppert, Edward E.; Fox, Richard S, & Barnes, Robert D. (2004), Invertebrate zoology : a functional evolutionary approach (7th ed.), Belmont, CA: Thomson-Brooks/Cole, ISBN 978-0-03-025982-1 , p. 788ff. – see particularly p. 804 ^ Pechenik, Jan A. (2005). Biology of the invertebrates. Boston: McGraw-Hill, Higher Education. p. 178. ISBN 0-07-234899-2.  ^ 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. ISBN 0-03-056747-5.  ^ a b Robert Lee Wallace. "Rotifers: Exquisite Metazoans". 2002. doi: 10.1093/icb/42.3.660 quote: "What is the function of the retrocerebral organ?" ^ Jessica L. Mark Welch, David B. Mark Welch & Matthew Meselson (10 February 2004). "Cytogenetic evidence for asexual evolution of bdelloid rotifers". Proceedings of the National Academy of Sciences. 101 (6): 1618–1621. Bibcode:2004PNAS..101.1618W. doi:10.1073/pnas.0307677100. PMC 341792 . PMID 14747655.  ^ a b c Nogrady, T., Wallace, R.L., Snell, T.W., 1993. Rotifera
vol.1: biology, ecology and systematics. Guides to the identification of the microinvertebrates of the continental waters of the world 4. SPB Academic Publishing bv, The Hague. ^ Claus-Peter Stelzer, Johanna Schmidt, Anneliese Wiedlroither & Simone Riss (20 September 2010). "Loss of sexual reproduction and dwarfing in a small metazoan". PLoS ONE. 5 (9): e12854. Bibcode:2010PLoSO...512854S. doi:10.1371/journal.pone.0012854. PMC 2942836 . PMID 20862222. CS1 maint: Multiple names: authors list (link) ^ Wurdak, E.S., Gilbert, J.J., Jagels, R., 1978. Fine structure of the resting eggs of the rotifers Brachionus
calyciflorus and Asplanchna sieboldi. Transactions of the American Microscopical Society 97 (1), 49-72. ^ Clément, P., Wurdak, E., 1991. Rotifera. In: Harrison, F.W., Ruppert, E.E. (Eds.), Microscopic Anatomy of Invertebrates. Aschelminthes, vol. IV. Wiley-Liss, 219-297. ^ Marcus, N.H., Lutz, R., Burnett, W., Cable, P., 1994. Age, viability and vertical distribution of zooplankton resting eggs from an anoxic basin: evidence of an egg bank. Limnology and Oceanography 39 (1), 154-158. ^ Kotani, T., Ozaki, M., Matsuoka, K., Snell, T.W., Hagiwara, A., 2001. Reproductive isolation among geographically and temporally isolated marine Brachionus
strains. Hydrobiologia 446-447, 283-290. ^ García-Roger, E.M., Carmona, M.J., Serra, M., 2005. Deterioration patterns in diapausing egg banks of Brachionus
(Müller, 1786) rotifer species. Journal of Experimental Marine Biology and Ecology 314, 149-161. ^ 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. doi:10.1111/jeb.12326. PMID 25105197.  ^ 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 ^ Flot, Jean-François; Hespeels, Boris; Li, Xiang; Noel, Benjamin; Arkhipova, Irina; Danchin, Etienne G. J.; Hejnol, Andreas; Henrissat, Bernard; Koszul, Romain; Aury, Jean-Marc; Barbe, Valérie; Barthélémy, Roxane-Marie; Bast, Jens; Bazykin, Georgii A.; Chabrol, Olivier; Couloux, Arnaud; Da Rocha, Martine; Da Silva, Corinne; Gladyshev, Eugene; Gouret, Philippe; Hallatschek, Oskar; Hecox-Lea, Bette; Labadie, Karine; Lejeune, Benjamin; Piskurek, Oliver; Poulain, Julie; Rodriguez, Fernando; Ryan, Joseph F.; Vakhrusheva, Olga A.; Wajnberg, Eric; Wirth, Bénédicte; Yushenova, Irina; Kellis, Manolis; Kondrashov, Alexey S.; Mark Welch, David B.; Pontarotti, Pierre; Weissenbach, Jean; Wincker, Patrick; Jaillon, Olivier; Van Doninck, Karine (21 July 2013). "Genomic evidence for ameiotic evolution in the bdelloid rotifer Adineta vaga". Nature. 500 (7463): 453–457. Bibcode:2013Natur.500..453F. doi:10.1038/nature12326.  ^ Stelzer, C.P. (2011). A first assessment of genome size diversity in Monogonont rotifers. Hydrobiologia 662: 77–82 http://www.springerlink.com/content/u6115421878k4425 ^ Stelzer, C.P., Riss, S., Stadler, P. (2011) Genome size evolution at the speciation level: The cryptic species complex Brachionus plicatilis (Rotifera) BMC Evolutionary Biology 11: 90.

Jersabek, C. D. & Leitner, M. F.2013: The Rotifer
World Catalog. World Wide Web electronic publication. [1]

External links[edit]

Wikimedia Commons has media related to Rotifera.

has information related to Rotifera

The Wikibook Dichotomous Key has a page on the topic of: Rotifera

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

v t e

Extant Animal

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

A n i m a l i a

Porifera (sponges)

Diploblasts (Eumetazoa)

(comb jellies)




(jellyfish and relatives)

Bilateria (Triploblasts)

(see below↓)



Xenoturbellida (Xenoturbella) Acoelomorpha

acoels nemertodermatids

N e p h r o z o a



lancelets tunicates craniates / vertebrates


Echinodermata (starfish and relatives) Hemichordata

acorn worms pterobranchs

P r o t o s t o m i a



(mud dragons) Priapulida
(penis worms)



Nematoda (roundworms) Nematomorpha
(horsehair worms)




Arthropoda (arthropods) Tardigrada (waterbears) Onychophora
(velvet worms)

S p i r a l i a


(arrow worms) Gnathostomulida (jaw worms) Micrognathozoa (Limnognathia) Syndermata

Rotifera Acanthocephala




Orthonectida Dicyemida
or Rhombozoa


Platyhelminthes (flatworms) Gastrotricha (hairybacks)


Cycliophora (Symbion) Mollusca


Annelida (ringed worms) Nemertea
(ribbon worms)



or Kamptozoa Ectoprocta (moss animals)


Brachiopoda (lamp shells) Phoronida (horseshoe worms)

Major groups within phyla


Calcareous Hexactinellid Demosponge Homoscleromorpha


inc. corals Medusozoa
inc. jellyfish Myxozoa


Jawless fish Cartilaginous fish Bony fish Amphibians Reptiles/Birds Mammals


Sea lilies Asterozoa
inc. starfish Echinozoa


Chromadorea Enoplea Secernentea


Chelicerates/Arachnids Myriapods Crustaceans Hexapods/Insects


Turbellaria Trematoda Monogenea Cestoda


Phylactolaemata Stenolaemata Gymnolaemata


Polychaetes Clitellata Echiura


Gastropods Cephalopods Bivalves Chitons Tusk shells

Phyla with ≥5000 extant species bolded See also Diploblasts Monoblastozoa (nomen dubium)


v t e

Antonie van Leeuwenhoek

Microscopic discoveries 1

Microscopic organisms

Bacteria Ciliate Giardia Infusoria Protist Protozoa Rotifer Volvox


(sperm cells) Red blood cells Crystals
in gouty tophi

General topics

Animalcule Bacteriology Protozoology Protistology Spontaneous generation Preformationism Microscopic discovery of microorganisms Microscopic scale History of biology History of microbiology Natural history Optical microscopy History of microscopy History of the microscope Invention of the optical microscope Timeline of microscope technology Golden Age of Dutch science and technology Science and technology in the Dutch Republic Royal Society Scientific Revolution Age of Reason

Related people

Clifford Dobell
Clifford Dobell
(Leeuwenhoek scholar) Brian J. Ford (Leeuwenhoek scholar) Galileo Galilei Regnier de Graaf Robert Hooke
Robert Hooke
(author of Micrographia) Nicolaas Hartsoeker Nicolas Steno Jan Swammerdam Johannes Vermeer


Antoni van Leeuwenhoek Ziekenhuis Leeuwenhoek (crater) Leeuwenhoek Lecture Leeuwenhoek Medal Leeuwenhoeckia Levenhookia Leeuwenhoekiella List of people considered father or mother of a scientific field

1 First observed, described, and studied by van Leeuwenhoek.

Taxon identifiers

Wd: Q180148 ADW: Rotifera EoL: 6851 EPPO: 1ROTIP Fauna Europaea: 12167 Fossilworks: 67114 iNaturalist: 126917 ITIS: 58239 NCBI: 10190