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Thebraingivesrisetoavaryingnumberofpairednerves.Theforward-lead-
ingnervesincludethoseextendingtothesensoryorgansandapairofthepharyn-
gealnerves.Bothsidesofthebraingiverisetotwothicknerves,runningdorsally
anddirectedtowardstheposteriorend,whichterminateinthedorsalantennae,
thetwothinnerventralnervesextendingtothelateralantennae.Thethreemain
ganglia(pharyngeal,subpharyngeal,andpedal)areinterconnectedbylongitudi-
nalnerves,branchingintodelicatenervefibresleadingtomusclesandinternal
organs(Fig.14).
Therotifersenseorgansarerelativelysimple.Theyarefrequentlyrepre-
sentedbysinglesensorycells,antennae,orciliatednodesontheheadwithin
thecorona(Figs6,14).Themostimportantsenseorgansincludemechano-and
chemoreceptors,extremelyusefulinrecognisingthesizeandqualityoffoodpar-
ticles(SNELL1998)iRotifersinterceptchemicalinformationfromalgaeandare
sensitivetoalkaloidsproducedbycyanobacteria.Inaddition,theyarecapableof
receivingsignalsfromotheranimals,mostimportantlyfrompredatorsandcon-
specificindividuals.
Mostrotiferspossessphotoreceptorsintheformofsimplepigmentspecks
locatedinthelowerpartofthebrain.Suchspecksmayalsooccurapicallyor
laterallyonthebody,atthebaseoftheciliaryapparatusinthelattercase(an
unpairedcerebraleye,pairedlateraleyesorpairedcerebraleyesonthehead).
Theeyespots,ortheso-calledeyes,consistofsensorycells,frequentlyared-pig-
mentedcell,andcircularterminalcellsthatresemblelenses(STORCHandWELSCH
1991).Rotifershavealsotheretrocerebralorgan,locatedbelowthebrainand
shapedlikeasacwhichmay,albeitseldom,containstronglylight-refractorygran-
ules.Theretrocerebralorganopenswithinthecoronaandisassociated,insome
unexplainedmanner,withtheeyespots.
Excretoryandreproductivesystems.Theexcretorysystemconsistsof
pairedprotonephridiaofatypesimilartothatfoundinplathelminths.Thethin
lateralcanaliculiterminatein4-5flamecells.Themainductsendinacontractile
vesicle(urinarybladder)openingintothecloaca(Fig.1).
Themonogonontfemalereproductivesystemismadeupofasingleova-
ryconsistingoftwoparts:theovaryproper(germarium),thevitellarium,and
theoviduct(oviductus).Thesmallgermariumistobefoundlaterallyinthebody
orinsidethelargevitellarium,asyncytialformationwitheightlargenuclei.
Thereproductivecellsforminginthegermariumarepassedtothevitellariumto
beosmoticallyfedthere.Theovarygradesintotheoviduct,ashort,thin-walled
conduit;insomeviviparousrotifers(e.g.,Asplanchna),theoviductfunctionsas
auterus.Theoviductopensintothecloaca(Fig.1).
Morphologyandanatomyofrotifermales.Comparedtothefemales,ro-
tifermalesaresmall(40to500um),theirbodyplanbeinggreatlysimplified
bytheabsenceofthealimentarytractand,frequently,thelackoftheexcretory
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