Animal Diversity Web

Di­ver­sity

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)

Ge­o­graphic Range

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)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• oriental
  • native
• ethiopian
  • native
• neotropical
  • native
• australian
  • native
• oceanic islands
  • native
• arctic ocean
  • native
• indian ocean
  • native
• atlantic ocean
  • native
• pacific ocean
  • native
• mediterranean sea
  • native

• Other Geographic Terms
• holarctic
• cosmopolitan

Habi­tat

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)

• Habitat Regions
• temperate
• tropical
• terrestrial
• saltwater or marine
• freshwater

• Terrestrial Biomes
• tundra
• taiga
• desert or dune
• savanna or grassland
• chaparral
• forest
• rainforest
• scrub forest
• mountains

• Aquatic Biomes
• pelagic
• benthic
• reef
• lakes and ponds
• rivers and streams
• temporary pools
• coastal
• brackish water

• Wetlands
• marsh
• swamp
• bog

• Other Habitat Features
• riparian
• estuarine
• intertidal or littoral

Sys­tem­atic and Tax­o­nomic His­tory

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)

• Synapomorphies

  • syncytial integument
  • basal bodies of cilia composed of microtubule doublets, rather than triplets
  • anteriorly-directed sperm flagellum

Phys­i­cal De­scrip­tion

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)

• Other Physical Features
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• female larger

De­vel­op­ment

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)

Re­pro­duc­tion

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)

• Mating System
• monogamous

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)

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• parthenogenic
• sexual
• fertilization
  • internal
• oviparous
• embryonic diapause

Ro­tifers ex­hibit no parental in­vest­ment be­yond egg and ga­mete pro­duc­tion. (Br­usca and Br­usca, 2003)

• Parental Investment
• no parental involvement

Lifes­pan/Longevity

Ro­tifers are short-lived; their total lifes­pan has been recorded at 6 to 45 days. ("Ro­tifers", 2003)

Be­hav­ior

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)

• Key Behaviors
• natatorial
• diurnal
• nocturnal
• crepuscular
• parasite
• sessile
• motile
• sedentary
• solitary
• colonial

Com­mu­ni­ca­tion and Per­cep­tion

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)

• Communication Channels
• tactile
• chemical

• Perception Channels
• visual
• tactile
• vibrations
• chemical

Food Habits

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)

• Primary Diet
• carnivore
• herbivore
• omnivore
• planktivore
• detritivore

• Foraging Behavior
• filter-feeding

Pre­da­tion

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)

• Known Predators

  • long-tailed ducks (Clangula hyemalis)
  • red-throated loons (Gavia stellata)
  • glaucous gulls (Larus hyperboreus)
  • skuas (Stercorarius)
  • common eiders (Somateria mollissima)
  • dragonflies and damselflies (Order Odonata, Class Insecta)
  • thread-horn flies (Suborder Nematocera, Class Insecta)
  • glassworms (Chaoborus flavicans)
  • copepods (Epischura, Mesocyclops, Acanthocyclops)
  • nematodes (Phylum Nematoda)
  • bladderworts (Utricularia)
  • Rhizophydium gibbosum (Division Chytridiomycota, Kingdom Fungi)
  • rotifers (Asplanchna)

Ecosys­tem Roles

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)

• Ecosystem Impact
• parasite

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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)

• Positive Impacts
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of ro­tifers on hu­mans.

Con­ser­va­tion Sta­tus

As a broadly cos­mopoli­tan phy­lum, ro­tifers in gen­eral are not con­sid­ered en­dan­gered or threat­ened in any way. ("Ro­tifera", 2012)

• IUCN Red List [Link]

  Not Evaluated

Con­trib­u­tors

Je­remy Wright (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Leila Si­cil­iano Mar­tina (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Ref­er­ences

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