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Havingreviewedampleliteraturedataonreproductivebiologyofmonogon-
ontrotifers,NOGRADYetal.(1993)publishedtheirversionofthelifecycleofthose
microinvertebrates(Fig.18B).Stillanotherconceptofheterogony(Fig.18C)
wasputforwardbyWALLACEandRICCI(2002)whobaseditonphysiologicaland
geneticalresearchonrotiferreproduction,conductedinmanyEuropeancountries
andinNorthAmerica(BOGOSLOVSKIj1959,1960,1961;PEjLER1957;GILBERT
1966;POURRIOTandCLEmENT1981;SNELLandHOFF1985;LUBZENSetal,1989).
Thedifferentideasontherotiferlifecycle,presentedabove,testifytoahigh
plasticityofrotiferreproduction.Allthoseideas,however,donotruleouttheva-
lidityofthefirstdescriptionofheterogonyinmonogonontrotifers(BIRKY1964).
Doubtless,itisimportantthatheterogonyhastoinvolveasexual(gamogenic)
cycle.Intheopinionofnumerousauthors,thecyclicityisrelatedtothevariability
ofbothabioticandbioticenvironmentalconditions(e.g.,temperature,oxygen
content,pH,qualityandquantityofavailablefoodresources,etc.).
Dependingonitsgeographicallocationandspecificfeaturesofthewater
bodyitinhabits,aspeciesmayproduceadifferentnumberofparthenogeneticand
gamogenicgenerations.Thoseformshavingasinglesexualgenerationperyear
aretermedmonocyclic;thoseproducingtwosexualgenerationsareknownas
dicyclic,whilenumeroussexualgenerationsperyearmakesaspeciespolycyclic.
Mostplanktonicrotifersaredicyclic.Theirgamogenesisoccursusuallytwice
ayear,inspringandinautumn,frequentlyinsynchronywithpeaksofabundance.
Monocyclicityisnotespeciallyfrequentamongwarm-waterrotiferspecies
widelydistributedinnorthernlatitudes,suchasBrachionusangularis.Anexcep-
tionisfurnishedbyMonimotrochawhichusuallyinhabitdeepoligotrophiclakes
orthelittoralheavilyvegetatedbymacrophytes.
Insummary,ithastobereiteratedthattherotiferfemales,regardlessof
thehowmanyfemaletypesthereare,layeggsofthefollowingthreetypes:
-mictic“male”eggsthathatchintomalesandthe“female”eggsgivingriseto
micticfemalesonly;
-amicticeggs(theso-calledsummereggs)hatchingintoamicticfemales;
-mictic,fertilised,dormanteggs(theso-calledwintereggs)thatgiveriseto
amicticfemales.
Duetotheirlongpersistencetime,dormanteggsareprovidedwiththick
membranesensuringprotectionfromsuddenchangesinenvironmentalcondi-
tions.Themembranesofamicticeggsarethinsothattheeggsmaydevelopdur-
ingafewhoursorafewdaysaftertheyhavebeenlaid.
MalesoccurinthelifecycleofrotifersrepresentingtheclassesSeisonidea
andMonogononta.Sofar,theyhavenotbeenfoundintheBdelloidea.Noteworthy
isthewell-developedcopulatoryapparatusinmonogonontrotifermales(Fig.15).
Copulationinmonogonontrotifersproceedsineitherofthefollowingtwo
ways:
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