Phylum Rotifera is comprised of two classes, Eurotatoria (which includes orders Monogononta and Bdelloidea) and Seisonidea, with over 2,200 currently known species. They are most commonly found in freshwater, although some species live in brackish or marine habitats, in soil, or on mosses. Rotifers may be sessile or sedentary and some species are colonial. Their bodies can be clearly divided into three regions: head, trunk, and foot, but the body surface varies widely between species, some even have spines or tubercles and/or a protective casing (lorica). Some species sexually reproduce, but parthenogenic reproduction is far more common, order Bdelloidea lacks males altogether. Rotifers mainly feed on smaller animals, algae, and organic particulates, although some species are parasitic. Depending on the species, they filter feed or actively hunt and capture prey. (Brusca and Brusca, 2003; Ruppert, et al., 2004; Segers, 2007; Wallace, 2002; Zhang, 2011)
Rotifers are considered broadly cosmopolitan, and are found in marine, brackish, and fresh waters throughout the world, excluding Antarctic. Several species are endemic to specific regions. (Brusca and Brusca, 2003; Segers, 2007)
The majority of rotifers are planktonic and are found in freshwater environments, though many are found in water films and droplets within soil, lichens and mosses. Members of order Seisonidea are known only from marine environments and live on the bodies of leptostracan crustaceans. Other marine rotifers are mainly littoral, but have been found at depths of 400 m and greater. All members of family Flosculariidae (class Monogononta), about 25 species, are colonial; colonies may be sessile or free-swimming, colony members do not appear to share resources. A few species are known endo- or ectoparasites. (Brusca and Brusca, 2003; Hyman, 1951; Segers, 2007; Wallace, 2002)
Phylum Rotifera was formally named by Georges Cuvier in 1817, although several species had been documented and described by authors such as John Harris, Anton von Leeuenhoek, and Louis Joblot in the late 17th and early 18th century. Classes Monogononta and Bdelloidea were erected in the late 1800s by Plate and Hudson. No synonyms exist for the phylum, or any of its included classes. (Harmer and Shipley, 1896; Zhang, 2011)
The three currently recognized classes of rotifers, along with acanthocephalans (formerly considered their own phylum) form the clade Syndermata. Molecular phylogenetic analyses have suggested Syndermata is the sister group to phylum Gnathostomulida (jaw worms), forming the Gnathifera clade. This analysis, along with a separate study (which did not include gnathostomulids), placed rotifers within superphylum Lophotrochozoa, as a possible sister group to phylum Platyhelminthes (flatworms). (Paps, et al., 2009; Weber, et al., 2013; Zrzavy, 2001)
Relationships within Syndermata are still under debate. Morphological characters support the sister relationship of monogononts and bdelloids in class Eurotatoria. Molecular studies, however, have suggested that bdelloids are more closely related to acanthocephalans. The position of Seisonidea is even more contentious, with authors alternately suggesting they represent the sister group to all other Syndermata, to the Acanthocephala and Bdelloidea clade, or to just Acanthocephala, instead of Bdelloidea. (Ahlrichs, 1995; Garcia-Varela and Nadler, 2006; Kristensen, 2002; Ruppert, et al., 2004; Zrzavy, 2001)
These animals are small, most are less than 1 mm long, although a few species reach lengths up to 3 mm. They have many different body forms, ranging from sac-shaped to spherical or cylindrical, wide and flattened, or long and slender. They can be easily divided into three regions: head, trunk, and foot, although the foot may be modified or absent, depending on whether the species is sedentary or free swimming. Body surface appearance varies; some species have spines or tubercles and/or a protective casing (lorica). The skeletal lamina, a layer within the animal’s epidermis, produces the lorica (if present), as well as any other surface structures. Many rotifers also have a gelatinous layer outside the epidermis. Some have dorsal or lateral sensory antennae. Many have bodies that are annulated to increase flexibility. In most species, males are extremely rare, and are completely absent in bdelloid species. When they are present, male rotifers tend to be much smaller, shorter lived, and less complex than females. (Brusca and Brusca, 2003; Ruppert, et al., 2004; Wallace, 2002)
These animals are eutelic, with an average cell count of 900 to 1,000. Rotifers are blastocoelomates, and body support and shape are maintained not by a muscular body wall but by the skeletal lamina and the fluid-filled body cavity itself. Organs are suspended within the blastocoel. Longitudinal muscle bands are present, which serve mainly to retract protruding body parts such as the foot. In sessile species, swimming is achieved by ciliate movement and/or using the foot in a “creeping” fashion: attaching the foot with secretions from its pedal glands, extending its body, attaching its head to substrate, then releasing the foot and using its muscle bands to move its body forward. In sedentary species, pedal gland secretions cement the rotifer in place. (Brusca and Brusca, 2003; Ruppert, et al., 2004; Wallace, 2002)
All rotifer species have a ciliary organ located on the head, known as a corona, which is typically used for locomotion and feeding. It is from these cilia and their characteristic motion, resembling turning wheels, that this phylum derives its common name, 'wheel animals'. The appearance of the corona varies from species to species. In its simplest form, the corona is made of the circumoral field, also known as the buccal field, which surrounds the rotifer’s mouth, located anteroventrally. The area of the head anterior to this ring is known as the apical field. In many species, the corona is made up of two concentric rings, the trochus (most anterior) and cingulum, which may itself be made up of rings of cilia called trochal discs. The cilia of the trochus and cingulum move asynchronously. (Brusca and Brusca, 2003; Ruppert, et al., 2004; Wallace, 2002)
Although feeding mechanisms vary, general digestive structures are largely the same between species. The anterior portion of the digestive system consists of the corona, a muscular pharynx (mastax), and trophi (chitinous jaws). Some may have a buccal tube leading from the mouth to the pharynx. These animals have two to seven salivary glands, which secrete digestive enzymes and lubricate food material. An esophagus connects the mastax to the stomach, where a pair of gastric glands secretes enzymes to further break down food matter, and absorption of nutrients occurs. The short intestine is connected to the anus via a cloaca. A nephridioduct leads from a pair of flame bulb protonephridia (located much farther forward in the body); these empty into a collecting bladder, which also empties into the cloaca. This system controls osmoregulation and expels nitrogenous by-products of digestion. Waste, gases and nutrients are all diffused directly to the exterior environment through organ tissues and blastocoelomic fluid. (Brusca and Brusca, 2003; Hyman, 1951; Ruppert, et al., 2004; Wallace, 2002)
Once eggs are fertilized, they develop a multi-layered membranous shell and are either attached to substrate, or carried (externally or internally) by the female. Some species alternate parthenogenic and sexual reproduction. In these cases, females produce diploid eggs (amictic ova) during favorable conditions, which develop without fertilization. If conditions become less favorable, these eggs grow into mictic females who produce haploid (mictic) ova; these ova may develop, via parthenogenesis, into males. When they mate, these males produce hardy zygotes that hatch into amictic females. It is thought that embryos undergo modified spiral cleavage; unequal holoblastic early cleavage produces a sterobastula. Development is direct, although some sessile species produce free-swimming "larvae" that settle quickly. There is no cell division following embryonic stages, as these species are eutelic. Each species may have alternative adult morphotypes due to differing ecological conditions, a phenomenon known as developmental polymorphism. (Brusca and Brusca, 2003; Hyman, 1951; Wallace, 2002)
Parthenogenesis is the most common method of reproduction in rotifers. In sexually reproducing species, a male either inserts his copulatory organ into a female’s cloaca or attaches to her, injecting sperm through the body wall directly into the blastocoel. When present, males are short-lived and have a greatly reduced gut. (Brusca and Brusca, 2003; Wallace, 2002)
Rotifers are dioecious, but in most species, males are extremely rare or even unknown. Male rotifers, when present, most often have a single testis, which is connected to a sperm duct and a posterior gonopore, which is unconnected to the digestive system. Most females have paired or single germovitellaria that provides eggs (produced in ovaries) with yolks. Yolked eggs pass through an oviduct to the cloaca. In species with sexual reproduction, a male either inserts his copulatory organ into a female’s cloaca or attaches to the female, injecting sperm through the body wall directly into the blastocoelom. Depending on environmental conditions, eggs may be mictic or amictic. No particular breeding season is associated with these animals. Females may parthenogenetically produce up to seven eggs at a time, eggs hatch within 12 hours. Sexual maturity is reached very quickly, within 18 hours of hatching. If conditions are unfavorable, mictic ova with thick shells are more likely to be produced. Mictic eggs are able to survive desiccation, low temperatures, and other unfavorable environmental conditions. These ova undergo a period of diapause and do not hatch until conditions are more favorable. (Brusca and Brusca, 2003; Hyman, 1951; Marini, 2002)
Rotifers exhibit no parental investment beyond egg and gamete production. (Brusca and Brusca, 2003)
Rotifers are short-lived; their total lifespan has been recorded at 6 to 45 days. ("Rotifers", 2003)
Most rotifers are motile and planktonic; swimming is achieved by ciliary movement. Motile rotifers may also move by "creeping" along the bottom, attaching the foot with secretions from the pedal glands, extending the body, attaching the head to substrate, then releasing the foot and using muscle bands to move the body forward. In sedentary species, pedal gland secretions cement the rotifer into place. Some rotifers also have moveable extremities (bristles, setae, etc.), which they use for quick movement. (Brusca and Brusca, 2003; Hyman, 1951; Wallace, 2002)
The coronal/apical areas of rotifers have sensory bristles and often paired cilial pits as well, which are thought to be chemoreceptive. It is common for these animals to have at least one photosensitive pigment cup ocellus on the dorsal or ventral side of the cerebral ganglion and many species have one or two pairs of ocelli. Some may have lateral or apical ocelli that are also photosensitive. Some rotifers have sensory hairs on their antennae, or the antennae themselves may be comprised of sensory hairs. (Brusca and Brusca, 2003; Hyman, 1951; Wallace, 2002)
Filter feeding rotifers have well-developed coronal cilia and a mastax (pharynx) for grinding food. The cilia produce a feeding current, drawing particles into a ciliated feeding groove, which carries them to the buccal field. Raptorial rotifers grasp or pierce food items with pincer-like mastax “jaws”, which may then be used to grind up food particles. Some rotifers feed by trapping prey; these have a funnel-shaped corona lined with long immotile bristles or spines rather than cilia. When a prey item enters the funnel, the bristles or spines keep it from escaping and it is drawn into the mouth, usually located in the center of the funnel. Finally, some rotifers gather food using coronal tentacles and others are symbiotic, typically with crustaceans, or entoparasites of annelids and terrestrial slugs, snail egg cases, freshwater algae, and, in one species, a colonial protist (Volvox). Rotifers typically feed on protozoa, algae, bacteria, phytoplankton, nannoplankton, and detritus or other organic matter. ("Rotifera", 2012; Brusca and Brusca, 2003; Hyman, 1951)
As planktonic animals, adult rotifers and their eggs serve as prey to many larger animals, including birds, insects and insect larvae, bugs, beetles, water fleas, copepods, nematodes, carnivorous plants, fungi, and other rotifers. ("Rotifera", 2012; Brusca and Brusca, 2003)
As mainly planktonic organisms, rotifers provide food to many other animals. Adults and eggs may be parasitized by fungi. Some rotifers are symbiotic with, or parasitic on, other organisms. Members of the genera Seison and Paraseison live on the legs and gills of Nebalia, a genus of marine leptostracan crustaceans, feeding on their host's eggs and detritus. Members of genus Embata are known to live in the gills of amphipods and decapods. Some rotifers are endoparasitic (sometimes epizoic), mainly on invertebrates including crustaceans, brachiopods, algae, protists, bacteria, bryozoans, other rotifers, sponges, fungi, mosses, snail eggs, annelids, oligochaetes, and slugs. ("Rotifera", 2012; Brusca and Brusca, 2003; Glime, 2010; May, 1989; Segers, 2007)
As mainly planktonic animals, rotifers are an important food source for many animals, including some that are economically important to humans. They are also studied by scientists around the world. ("Rotifera", 2012)
There are no known adverse effects of rotifers on humans.
As a broadly cosmopolitan phylum, rotifers in general are not considered endangered or threatened in any way. ("Rotifera", 2012)
Jeremy Wright (author), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Animal Diversity Web Staff.
the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.
areas with salty water, usually in coastal marshes and estuaries.
an animal that mainly eats meat
Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.
uses smells or other chemicals to communicate
the nearshore aquatic habitats near a coast, or shoreline.
used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.
having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.
active at dawn and dusk
in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.
an animal that mainly eats decomposed plants and/or animals
At about the time a female gives birth (e.g. in most kangaroo species), she also becomes receptive and mates. Embryos produced at this mating develop only as far as a hollow ball of cells (the blastocyst) and then become quiescent, entering a state of suspended animation or embryonic diapause. The hormonal signal (prolactin) which blocks further development of the blastocyst is produced in response to the sucking stimulus from the young in the pouch. When sucking decreases as the young begins to eat other food and to leave the pouch, or if the young is lost from the pouch, the quiescent blastocyst resumes development, the embryo is born, and the cycle begins again. (Macdonald 1984)
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
union of egg and spermatozoan
a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
mainly lives in water that is not salty.
An animal that eats mainly plants or parts of plants.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.
Found in northern North America and northern Europe or Asia.
fertilization takes place within the female's body
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
marshes are wetland areas often dominated by grasses and reeds.
Having one mate at a time.
having the capacity to move from one place to another.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.
an animal that mainly eats all kinds of things, including plants and animals
found in the oriental region of the world. In other words, India and southeast Asia.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
development takes place in an unfertilized egg
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
an animal that mainly eats plankton
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
mainly lives in oceans, seas, or other bodies of salt water.
scrub forests develop in areas that experience dry seasons.
remains in the same area
non-motile; permanently attached at the base.
Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa
reproduction that includes combining the genetic contribution of two individuals, a male and a female
a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.
uses touch to communicate
Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
breeding takes place throughout the year
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