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Which species of rotifer is this?

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If found this in a moss sample.


Rotifer

The rotifers ( / ˈ r oʊ t ɪ f ər z / , from Latin rota "wheel" and -fer "bearing"), commonly called wheel animals or wheel animalcules, [1] make up a phylum (Rotifera / r oʊ ˈ t ɪ f ər ə / ) 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 in 1703. [2] Most rotifers are around 0.1–0.5 mm long (although their size can range from 50 μm to over 2 mm), [1] and are common in freshwater environments throughout the world with a few saltwater species.

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.

In June 2021, biologists reported the restoration of bdelloid rotifers after being frozen for 24,000 years in the Siberian permafrost. [7]


Rotifera☆

Feeding

Rotifers use a variety of methods to procure their food. In filter or suspension feeding a microphagous animal consumes tiny algae, bacteria, yeast, and protists by creating filtering currents that bring small particles to its mouth (e.g., Brachionus, Keratella). Many rotifers that crawl over surfaces feed by a scraping action that removes food from the surface (e.g., certain bdelloids). Some large rotifers such as the planktonic genus Asplanchna and the sessile genera Collotheca and Cupelopagis feed by grasping and swallowing their prey whole (raptorial). A small number of rotifers are detritus feeders and a few are parasitic. Some consume a variety of foods, while others are extremely specific. Acyclus inquietus feeds on the eggs and young of the sessile rotifer Sinantherina socialis Trichocerca cylindrica sucks out the contents of the eggs of other rotifers.


Rotifers as models for the biology of aging

It has been two decades since 1993 when research on the biology of rotifer aging was last reviewed by Enesco. Much has transpired during this time as rotifer biologists have adapted to the "omics" revolution and incorporated these techniques into the experimental analysis of rotifers. Rotifers are amenable to many of these approaches and getting adequate quantities of DNA, RNA, and protein from rotifers is not difficult. Analysis of rotifer genomes, transcriptomes, and proteomes is rapidly yielding candidate genes that likely regulate a variety of features of rotifer biology. Parallel developments in aging biology have recognized the limitations of standard animal models like worms and flies and that comparative aging research has essentially ignored a large fraction of animal phylogeny in the lophotrochozoans. As experimentally tractable members of this group, rotifers have attracted interest as models of aging. In this paper, I review advances over the past 20 years in the biology of aging in rotifers, with emphasis on the unique contributions of rotifer models for understanding aging. The majority of experimental work has manipulated rotifer diet and followed changes in survival and reproductive dynamics like mean lifespan, maximum lifespan, reproductive lifespan, and mortality rate doubling time. The main dietary manipulation has been some form of caloric restriction, withholding food for some period or feeding continuously at low levels. There have been comparative studies of several rotifer species, with some species responding to caloric restriction with life extension, but others not, at least under the tested food regimens. Other aspects of diet are less explored, like nutritional properties of different algae species and their capacity to extend rotifer lifespan. Several descriptive studies have reported many genes involved in rotifer aging by comparing gene expression in young and old individuals. Classes of genes up or down-regulated during aging have become prime targets for rotifer aging investigations. Alterations of gene expression by exposure to specific inhibitors or RNAi knockdown will probably yield valuable insights into the cellular mechanisms of rotifer life extension. I highlight major experimental contributions in each of these areas and indicate opportunities where I believe additional investigation is likely to be profitable.

Figures

Figure 1. Comparative rotifer lifespan on different…

Figure 1. Comparative rotifer lifespan on different algae diets

Effects of different algae diets on…

Figure 2. Algae culture replacement rate affects…

Figure 2. Algae culture replacement rate affects rotifer survival and reproduction


Introduction to the Rotifera

Rotifers are microscopic aquatic animals of the phylum Rotifera. Rotifers can be found in many freshwater environments and in moist soil, where they inhabit the thin films of water that are formed around soil particles. The habitat of rotifers may include still water environments, such as lake bottoms, as well as flowing water environments, such as rivers or streams. Rotifers are also commonly found on mosses and lichens growing on tree trunks and rocks, in rain gutters and puddles, in soil or leaf litter, on mushrooms growing near dead trees, in tanks of sewage treatment plants, and even on freshwater crustaceans and aquatic insect larvae. (Örstan, 1999)

Because of their very small size and mostly soft bodies, rotifers are not commonly favored for fossilization. Their only hard parts, their jaws, might be preserved in the fossil record, but their tiny size makes detection a serious challenge (Örstan, 1999). However, fossils of the species Habrotrocha angusticollis have been found in 6000 year old Pleistocene peat deposits of Ontario, Canada (Warner et al., 1988). The oldest reported fossil rotifers have been found in Dominican amber dating to the Eocene (Waggoner & Poinar, 1993).

Rotifers are multicellular animals with body cavities that are partially lined by mesoderm. These organisms have specialized organ systems and a complete digestive tract that includes both a mouth and anus. Since these characteristics are all uniquely animal characteristics, rotifers are recognized as animals, even though they are microscopic. Most species of rotifers are about 200 to 500 micrometers long. However a few species, such as Rotaria neptunia may be longer than a millimeter (Orstan 1999). Rotifers are thus multicellular creatures who make make their living at the scale of unicellular protists.

As rotifers are microscopic animals, their diet must consist of matter small enough to fit through their tiny mouths during filter feeding. Rotifers are primarily omnivorous, but some species have been known to be cannibalistic. The diet of rotifers most commonly consists of dead or decomposing organic materials, as well as unicellular algae and other phytoplankton that are primary producers in aquatic communities. Such feeding habits make some rotifers primary consumers. Rotifers are in turn prey to carnivorous secondary consumers, including shrimp and crabs.

As well as their morphology and feeding habits, reproduction in rotifers is rather unusual. Several types of reproduction have been observed in rotifers. Some species consist only of females that producetheir daughters from unfertilized eggs, a type of reproduction called parthenogenesis. In other words, these parthenogenic species can develop from an unfertilized egg, asexually. Other species produce two kinds of eggs that develop by parthenogenesis: one kind forms females and the other kind develops into degenerate males that cannot even feed themselves (sexual dimorphism). These individuals copulate resulting in a fertilized egg developing within the rotifer. The males survive long enough to produce sperm that fertilize eggs, which then form resistant zygotes that can survive if the local water supply should dry up. The eggs are released and hatch in the water. If the egg develops in the summer, the egg may remain attached to the posterior end of the rotifer until hatching.

A particular class of rotifers called bdelloids can be found living in almost all freshwater environments, and occasionally in brackish and marine waters. Bdelloids are known for their remarkable ability to survive drying through a process known as cryptobiosis. Factors determining the duration of time that a rotifer is able to withstand desiccation include the humidity and temperature at which they are kept. Ideally, more humid conditions and mild to warm temperatures prevent the very dry conditions that are unfavorable to rotifers. Rotifer eggs can also withstand drying, with older embryos having a greater chance at survival (Örstan, 1999). The species Brachonius calyciflorus has been found to conserve energy when food is scarce by decreasing its respiration rate, while other species show no change in respiration rate. It is predicted that the ability of some rotifer species to adapt to resources with temporal variation in availability allows the coexistence of competing species of rotifers. Therefore, there is a tradeoff between the competitive ability of rotifers and the maximum population growth rate for a particular species. (Kirk, 1999).

Phylum Rotifera is divided into three classes: Monogononta, Bdelloidea, and Seisonidea. The largest group is the Monogononta, with about 1500 species, followed by the Bdelloidea, with about 350 species. There are only two known species of Seisonidea, which is usually regarded as the most "primitive", and in morphological analyses it comes out in a basal position (see cladogram at right).

Observing rotifers is relatively uncomplicated with the correct procedure and equipment. When extracting rotifers from a sample, it is best to use a pipette, drawing water from the area around clumps of soil or plant matter in the sample. The sample should be quickly transferred to a slide so the rotifers do not adhere to the sides of the pipette. Additionally, cover-slips should not be used under a light microscope because rotifers are easily disturbed and may contract into an indiscernible ball. If food is added to the slide, rotifers can be observed swimming if they do not become stuck to the slide (Ricci, 1999). Thus, although rotifers are invisible to the naked eye, they can easily be watched in their exported natural environments with the help of a microscope.

For more information about Rotifera:

    by Richard L. Howey by Mike Morgan , a movie filmed by amateur microscopist David Walker
    , an organization for scientists who study the really tiny animals like rotifers. by Richard Fox. A step-by-step tecaching exercise involving rotifers. study by James N. McNair, using rotifers in a chemostat. by Ron Neumeyer, a talented photomicroscopist who has taken some very nice rotifer portraits. , this time from Jerry Evans' information about Central Texas Natural History. , a wealth of free information on the collection, micromanipulation, and study of rotifers by Howard L. Taylor. , coordinated by Elizabeth Walsh of the University of Texas at El Paso. The site includes morphological and molecular phylogenies, a database, references, and basic information.

Image of Philodina kindly provided by Ron Neumeyer. Image of Epiphanes brachionus internal anatomy prepared by Elizabeth Walsh, of the University of Texas at El Paso, and used with permission. Pictures of Collotheca and Lecane kindly supplied by Wim van Egmond from the "Gallery of Rotifers" listed above. Image of living rotifer by Molly McCarthy of Ohio University.


Digestive System

The digestive system of Rotifers consists of the trophi and a gut. When prey is captured, it's first processed in a modified pharynx known as mastax. Also known as trophi, it's lined by chitinous material and looks like a translucent jaw. In the trophi, food material may be pierced or ground before being passed to the stomach through the esophagus.

For some of the species (e.g. members of the family Collothecidae), part of this structure is modified to form the proventriculus which acts as a food-storage organ. For the majority of species, food is digested in the stomach before being excreted through the anus.

For some of the species, e.g. members of genera Asplancha and Asplanchnopus, the gut ends in a blind stomach. As a result, waste material is excreted through the trophi.

* The trophi of given species are pigmented.


Rotifer Characteristics

❍ Rotifers are considered to be the smallest animals on Earth. Despite being 0.1 to 0.5 mm in size, they are made up of about a thousand cells.

❍ The term ‘rotifer’ does not refer to a single animal or species it is used for any of the 2,000 species that are included in the phylum Rotifera.

❍ Their body is divided into three sections – the head, trunk, and foot. Despite being microscopic creatures, they have jaws, a brain, stomach, intestines, testes/ovaries, and excretory organs.

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❍ The name ‘rotifer’ means ‘wheel-bearer’ in Latin. It is named so because it has two rings of cilia (hair-like structures) on its head, which, on moving, appear like two rotating wheels. They are also called ‘wheeled animals’.

❍ Most of them are aquatic, living in freshwater bodies, though a few are also found in saltwater. Some are also found on land, in puddles, rainwater drains, on algae, moss, moist soil typically anywhere a thin film of water is present.

❍ The outer covering is called the ‘cuticle’, which decides its appearance. Rotifers with a hard cuticle have a box-like appearance, while those with a flexible one seem worm-like. However, most species are long and somewhat cylindrical.

❍ The body wall is colorless, and therefore, all the organs are visible. The food present in the digestive system decides what color the animal takes on temporarily.

❍ The corona, or the rings of cilia on the head, are used to suck food into the mouth, or to move by creating water currents.

❍ Depending on the species, rotifers may either move through the water (called ‘planktonic’ rotifers), stay fixed permanently (called ‘sessile’), or creep like a worm.

❍ Planktonic rotifers use their foot to hold on to something while feeding. Sessile forms secrete an adhesive substance to stay attached permanently with their foot.

❍ Rotifers consume dead and decomposing substances, algae, bacteria, smaller rotifers typically anything they can fit inside their mouth. After ingesting, their trophi (jaws) crush the particles to make them smaller.

❍ These animals are eaten by fish and insect larvae, crustaceans, copepods (small crustaceans), tadpoles, and fish.

❍ The bodies are soft, and hence, do not turn into fossils. However, this property, along with their nutritious food habits, have made them a popular feed for fish larvae in aquaculture.

❍ Rotifers have a number of survival strategies. They can draw their corona and foot inside the cuticle on facing danger folding like a telescope. Some species also produce ‘resting eggs’, which can survive cold and drought for as long as 9 years. Other species survive the drying of ponds by contracting their bodies, and get revived as soon as conditions improve.

❍ Owing to their resilience, this group of animals has survived for 40 – 80 million years.

❍ Rotifers have extremely high reproductive rates. Many species reproduce without males, when eggs produced by the females directly hatch into juveniles (called parthenogenesis). All rotifers of the class Bdelloidea reproduce only by parthenogenesis, and males are absent altogether. Other species reproduce both, by sexual and asexual methods.

❍ In most species, females are much larger than males. The only function of males is to reproduce, and they lack any digestive organs. For this reason, they cannot eat, and survive only for a few hours.

❍ Rotifers are unique, in that, they are born with all their cells. So, unlike most animals, which grow by adding new cells, rotifers grow by increasing the size of their cells.

As can be seen, these animals clean up waste in water bodies, and provide food to various creatures in the wild. Thus, rotifers play an important ecological role, which cannot be overstated.

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Rotifers were first described when early microscopes became available, around 1700AD. [5] They are an important part of the freshwater zooplankton. Also, many species help decompose organic matter in soil. Rotifers eat fish waste, dead bacteria, and algae. They eat particles up to 10 micrometres in size. A rotifer filters 100,000 times its own volume of water per hour. They are used in fish tanks to help clean the water, to prevent clouds of waste matter.

About 2200 species of rotifers have been described. They are placed in the phylum Rotifera. This phylum is subdivided into three classes, Monogononta, Bdelloidea, and Seisonidea. The largest group is the Monogononta, with about 1500 species, followed by the Bdelloidea, with about 350 species. [6] There are only two known species of Seisonidea. [7] [8]

Fossils of the species Habrotrocha angusticollis have been found in 6000 year old Pleistocene peat deposits. [9] The oldest known fossil rotifers have been found in Eocene Dominican amber. [10]

The front has a ring of cilia circling the mouth. This gave the rotifers their old name of "wheel animalules". There is a protective lorica round its body, and a foot. Inside the lorica are the usual organs in miniturised form: a brain, an eye-spot, jaws, stomach, kidneys, urinary bladder.

Rotifers have a number of unusual features. Biologists suppose that these peculiarities are adaptations to their small size and the transient (fast changing) nature of its habitats.

Rotifers are specialists at living in habitats where water dries up regularly.

The Monogononta, which have males, produce fertilised 'resting eggs' which can resist desiccation (drought) for long periods. [11]

The Bdelloids, who have no males, contract into an inert form and lose almost all body water, a process known as cryptobiosis. Bdelloids can also survive the dry state for long periods: the longest well-documented dormancy is nine years. After they have dried, they may be revived by adding water. In this, and several other ways, they are a unique group of animals. [12]

Rotifers are hatched with a standard number of cell nuclei, exactly the same number for every rotifer in a species. This is called eutely. No cell division whatsoever takes place during adult life. [13] Not only that, but the number of nuclei in each tissue is constant. Furthermore, most of the nuclei do not have cell walls: rotifer tissue is largely or wholly a syncytium. [14]

Resisting radiation Edit

The absence of cell division is probably one reason they are extraordinarily resistant to ionising radiation. Also, repairing DNA is one of the things they are known to do after desiccation. [15]

Parthenogenesis Edit

In one of the classes, the freshwater Bdelloid rotifers, no males have ever been seen. It is the largest group of wholly parthenogenetic species in the Animalia.

The females in this group produce eggs by parthenogenesis (virgin birth). In some species these eggs develop into small juveniles before they are released from their parent. The offspring are clones of their mother.

Cytological and molecular genetic studies show that bdelloids evolved from a common ancestor which lost sexual recombination (meiosis and fertilisation) about 100 million years ago. [16] Research has also been done on the implications of parthenogenesis for speciation. [17]

Genetics Edit

Bdelloid rotifer genomes contain two or more non-identical copies of each gene. This suggests their asexual reproduction is of long standing. [18] For example, there are four copies of gene hsp82. Each is different and on a different chromosome. This cannot be explaned by normal gene duplication, which produces two or more near-identical genes next to each other. By contrast, in a monogont rotifer, most genes were single-copy. [19]

There are genes in bdelloid rotifers that seem to have come from bacteria, fungi, and plants. This suggests they arrived by horizontal gene transfer (HGT). The capture and use of exogenous (

foreign) genes seems to be important in bdelloid evolution. [20] [21] The team led by Matthew S. Meselson at Harvard University showed that, despite the lack of sexual reproduction, bdelloid rotifers do engage in genetic (DNA) transfer within a species or clade. The method used is not known at present. Bdelloid rotifers currently hold the 'record' for HGT in animals with

8% of their genes from bacterial origins. [22]

The Acanthocephala, a group of parasitic worms previously considered to be a separate phylum, have been shown to be modified rotifers. The exact relationship to the normal, freeliving, members of the phylum is not resolved. [14]


PHYLUM ROTIFERA

I. INTRODUCTION

The phylum Rotifera or Rotatoria comprises of approximately 2000 species of unsegmented, bilaterally symmetrical, pseudocoelomates, possessing two distinctive features ( Fig. 1 ). First, at the apical end (head) is a ciliated region called the corona, which is used in locomotion and food gathering. In adults of some forms, ciliation is lacking and the corona is a funnel or bowlshaped structure at the bottom of which is the mouth. Second, a muscular pharynx, the mastax, possessing a complex set of hard jaws, called trophi, is present in all rotifers.

FIGURE 1 . Lateral view of a generalized rotifer.

(Modified from Koste and Shiel, 1987 , with permission.) Copyright © 1987

When viewing the anterior end of most rotifers one is struck with the idea of a rotating wheel. This is due to the metachronal beat of cilia on the corona, a structure usually composed of two concentric rings: trochus and cingulum ( Fig. 2 ). This same image provided early microscopists with the name for the phylum: the etymon is Latin, rota, “wheel” and Latin, ferre, “to bear” equals “wheel bearers.” Although rotifers are often confused with ciliated protozoans and gastrotrichs by beginning students, those organisms do not possess trophi and their ciliation is not distributed in the same way as in rotifers. Rotifers are small organisms, generally ranging from 100–1,000 μm long, although a few elongate species may surpass 2,000 μm or more. Very few rotifers are parasitic ( May, 1989 ) nearly all are free-living herbivores or predators.

FIGURE 2 . Female and male Brachionus plicalitis.

(Modified from Pourriot, 1986 , with permission.) Copyright © 1986

Collectively this phylum is widely distributed, being found in all freshwater habitats at densities generally ranging up to about 1,000 individuals/L. However, rotifers occasionally become abundant if sufficient food is available, and can attain population densities of >5,000 individuals/L. In some rather unusual water bodies, exceedingly large populations can develop sewage ponds may contain about 12,000 individuals/L ( Seaman et al., 1986 ), and at certain times in soda water bodies in Chad, much more than 100,000 individuals/L may occur ( Iltis and Riou-Duvat, 1971 )! Although most inhabit freshwaters, some genera also have members that occur in brackish and marine waters. For example, about 20 of the 32 species comprising the genus Synchaeta are described as marine ( Nogrady, 1982 ). However, only about 50 species of rotifers are exclusively marine. In general, rotifers are not as diverse or as abundant in marine environments as microcrustaceans, but they occur in many nearshore marine communities ( Egloff, 1988 ) and occasionally comprise the dominant portion of the biomass ( Schnese, 1973 Johansson, 1983 ). One unusual group of rotifers, the bdelloids ( Fig. 3 ), may be found inhabiting the film of water covering mosses, lichens, and liverworts. Additionally, they are often abundant in soils ( Pourriot, 1979 ) estimates of their densities range from about 32,000 to more than 2 million individuals/m 2 , depending on soil moisture levels. Because of their feeding habits, and the fact that they are sometimes more numerous than nematodes, rotifers play an important role in nutrient cycling in soils ( Pourriot, 1979 ).

FIGURE 3 . Typical bdelloid rotifer (Philodina).

(Modified from several sources.)

Most rotifers are free-moving, either swimming as members of the plankton or crawling over plants or within the sediments however, some sessile species live permanently attached to freshwater plants ( Wallace, 1980 ). The vast majority of rotifers are solitary, but about 25 species form colonies of various sizes ( Wallace, 1987 ). All freshwater rotifers are either exclusively parthenogenetic or produce males for a limited time each year. Therefore, unless collections are made frequently, male rotifers may never be seen. Three very different classes of rotifers are commonly recognized (Seisonidea, Bdelloidea, Monogononta).

Additional accounts of this phylum may be found in most texts of general and invertebrate zoology, and in some specialized books about freshwaters ( Edmondson, 1959, pp. 420–494 Hutchinson, 1967, pp. 506–551 Pennak, 1989, pp. 169–225 ). For detailed reviews of the biology of rotifers consult the works of de Beauchamp (1965) , Hyman (1951, pp. 59–151) , Koste (1978) , Ruttner-Kolisko (1974) , and Nogrady et al. (1993) . In the 1800s there were some beautifully illustrated works that still offer an excellent view of these animals (e.g., Hudson and Gosse, 1886 ). There is no single scientific journal or set of journals in which researchers publish their work on rotifers the field is simply too diverse. However, every three years, since 1976, a small group of workers (approximately 50–100) have gathered to hold the International Rotifer Symposium. To date, nine such meetings have been held and most of the proceedings have been published as a special volume of the journal Hydrobiologia. Some of the papers discussed in this chapter were presented at those meetings.


The Anatomy of Rotifers

The body of a typical rotifer is divided into three main sections a head, trunk, and foot. Most rotifers are somewhat cylindrical in shape. They is a well-developed cuticle. The Rotifer cuticle is nonchitinous and is composed of sclerotized proteins This cuticle is either thick and rigid or thinner and more flexible. Rotifers with a more solid cuticle are referred to as ‘loricate’ and those with a more flexible cuticle are called ‘illoricate’. Loricate cuticles are usually made up of multiple plates, and often have spines, ridges, which are believed to be for protection against predators.

The most distinctive feature of rotifers is the presence of corona on the head. This is a ciliated structure that facilitates movement, allows feeding and from which the animals acquired their older name. The beating of the cilia, looks, quite often, like a wheel spinning. The main function of this corona of cilia is to draw water, and associated food particles, into the animal’s mouth.

After the head the main part of the body is the trunk. The trunk contains the internal organs including the stomach and the intestines. The final part of the body is the foot. This is usually much narrower than the head of the trunk, giving the appearance of a tail.

Some species of rotifers can retract the foot partially or wholly into the trunk. The foot ends in one to four toes. In free-swimming species the foot may be reduced in size or completely absent.

Digestive system

The coronal cilia generate a current that sweeps a continuous stream of food particles into the mouth. Behind the mouth are a variable number of salivary glands. From the mouth the food is passed to a powerful chewing pharynx called the ‘mastax’, This mastax contains a number of tiny, calcified, jaw-like structures called ‘trophi’, The form of the trophi vary between species. The actual structure of the trophi is related to the species feeding regime. Filter feeders tend to have more crushing, grinding trophi and predators biting grasping trophi.

From the mastax food is passed into the oesophagus and from there into the stomach. Most digestion and absorption occurs in the stomach. From the stomach the remains of the food pass into a short intestine. Finally wastes pass out of the body through an anus or cloaca.

A pair of protonephridia open into a bladder like organ that drains into the cloaca.

Nervous system

Rotifers usually possess several sets of sensory organs including one or two pairs of short antennae, two tiny sensory pits on the head, various sensory cilia and up to five eyes. The eyes are simple in structure, sometimes with just a single photoreceptor cell. All od these sensory structures are connected to a small brain, or cerebral ganglion which is located just above the mastax. A variable number of nerve cords extend from these ganglia down through the body. In many rotifers the nervous system amounts to up to about 25% of the roughly 1,000 cells that make up the animal’s body.


Rotifer

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Rotifer, also called wheel animalcule, any of the approximately 2,000 species of microscopic, aquatic invertebrates that constitute the phylum Rotifera. Rotifers are so named because the circular arrangement of moving cilia (tiny hairlike structures) at the front end resembles a rotating wheel. Although common in freshwater on all continents, some species occur in salt water or brackish water, whereas others live in damp moss or lichens. Most are free-living some are parasitic. Most live as individuals, but a few species form colonies. Most rotifers are only 0.1 to 0.5 mm (0.004 to 0.02 inch) long.

The body may be spherical, flattened, bag-like, or wormlike. The body wall consists of a thin cuticle. Tufts of cilia at the anterior end make up the corona, which is used for feeding and locomotion. Small organisms are extracted as food from water currents created by the ciliated corona. Larger organisms, such as other rotifers, crustaceans, and algae, are also eaten. A mouth and digestive tract are usually present. The muscular pharynx, or mastax, contains hard, tiny jaws. Members of each species consist of an exact number of cells.

In addition to the swimming rotifers, some (subclass Bdelloidea) loop along the bottom of ponds, alternately attaching the head and tail ends others remain anchored by means of tubes or cases of jelly attached to the bottom.

Modes of reproduction differ between species. Some species only reproduce parthenogenetically into females. Other species can reproduce both asexually and sexually, depending on environmental conditions. Males are smaller and less common in many species.



Comments:

  1. Taujora

    I have removed this phrase

  2. Khnemu

    Of course. And with this I have come across. We can communicate on this topic.

  3. Cingeswiella

    Are you joking?



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