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functioninglikeapenis(Fig.15).Infewrotiferspecies(e.g.,Brachionus),this
sectionofthespermductistransformedintoalongertube,linedwithathicker
cuticle,thatformsacopulatoryorganproper.
Stronglyretrogradedmaleslackthecopulatoryorgan,substitutedfunction-
allybytheposteriorendofthebody.Certainspeciesfeatureprostateglands,
varyinginshapeandsize.Malesproducetwotypesofspermatozoa:regularand
“stiff”,unabletomove.Copulationinvolvinginsertionofthecopulatoryorgan
throughthefemalecloacawasobservedinafewspeciesonly.Usually,thepenis
maypiercethefemalebodywallinanyplace,followingwhichthespermatozoa,
onceinthefemalepseudocoel,chemotacticallymigratetotheovaryandenterit.
5.Biology
Locomotion.Abilitytomoveisveryimportanttomostrotifersbecauseboth
feedingandreproductiondependonit.Allplanktonicrotifersswimincessantly;
epiphyticandbenthicrotifersareusuallyabletoswimaswell(exceptforafew
speciesoftheBdelloidea),whereassessilerotifershavefree-swimmingjuvenile
stages,thelarvae.Rotifersswimduetothemovementsofthecorona.Themanner
ofswimmingisverydistinct:theyusuallyfollowatrajectorywhichresembles
aprotractedspiral,andsimultaneouslyrotatethebody(Fig.16).Thespeedat
whichrotiferfemalesandmalesmovevariesanddependsonananimal’sageand
watertemperature.ThefastestmovementwasobservedinBrachionusplicatilis:
at+25oC,thefemalesmovedat0.6to0.9mm/s,thespeedofthemaleswas1.3to
1.5mm/s.Youngrotifersandoldfemaleswereseentoswimataspeedlowerby
30%thanthatattainedbymaturefemales.
TheusualswimmingspeedofthefemaleAsplanchnabrightwelliiandKera-
tellais0.9and0.5mm/s,respectively.Theswimmingspeedisimportantforfeed-
ingandfindingamatingpartner(EPPandLEWIS1984;GILBERTandKRIK1988).
Theswimmingspeedofsessilerotiferlarvaedependsontheirage.Larvaeof
Ptygurabeauchampiswimat2-2.5m/suntilabout3hold;theswimmingspeed
ofthoselarvaeolderthat4.5hisreducedtoabout1.0mm/s(WALLACE1980).
Importantforrotifermotilityarevariousprocessesonthebodyandtheirlength.
IndividualsofKeratellatestudothatlackposteriorprocessesswimataspeed
muchslowerthanthatshownbytheformsequippedwithsuchprocesses.Ow-
ingtoits12processes,calledfins,andthespecialstriatedmuscles,Polyarthra
isabletomoveatanimmensespeedof50mm/sandtoperformcharacteristic
leaps;theaverageswimmingspeedis35mm/s.Thisabilitytoswimveryfast
allowsPolyarthratoavoidthepredaciousAsplanchnaandtoescapethesuspen-
sion-feedingcrustaceans,e.g.,Daphnia(GILBERT1980a,1985a).Individualsof
thegeneraFiliniaandHexarthraarecapableofleapingrapidlyonaccountof
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