Earthworm

morphology of animals

1. EARTHWORM
dr.aarif

2. EARTHWORM
-Earthwormisareddishbrownterrestrialinvertebratethatinhabitstheupperlayerofthe
moistsoil.
-Duringdaytime,theyliveinburrowsmadebyboringandswallowingthesoil.
-Inthegardens,theycanbetracedbytheirfaecaldepositsknownaswormcastings.
-ThecommonIndianearthwormsarePheretimaandLumbricus.

3. EARTHWORM : Morphology
-Earthwormshavelongcylindricalbody.
-Thebodyisdividedintomorethanhundredshortsegments
whicharesimilar(metameresabout100-120innumber).
-Thedorsalsurfaceofthebodyismarkedbyadarkmedianmid
dorsalline(dorsalbloodvessel)alongthelongitudinalaxisof
thebody.
-Theventralsurfaceisdistinguishedbythepresenceofgenital
openings(pores).
-Anteriorendconsistsofthemouthandtheprostomium,alobe
whichservesasacoveringforthemouthandasawedgeto
forceopencracksinthesoilintowhichtheearthwormmay
crawl.
-Theprostomiumissensoryinfunction.

4. EARTHWORM : Morphology
CLITELLUM:
-Thefirstbodysegmentiscalledtheperistomium(buccalsegment)
whichcontainsthemouth.
-Inamatureworm,segments14-16arecoveredbyaprominentdark
bandofglandulartissuecalledclitellum.Itsecretesmucusandalbumen
fortheformationofcocoonoreggcapsule.
-Thusthebodyisdivisibleintothreeprominentregions–preclitellar,
clitellarandpostclitellarsegments
SETAE:
-Ineachbodysegment,exceptthefirst,lastandclitellum,therearerows
ofS-shapedsetae,embeddedintheepidermalpitsinthemiddleof
eachsegment.
-Setaecanbeextendedorretracted.
-Theirprincipalroleisinlocomotion

5. EARTHWORM : Morphology
APERTURES:
-Fourpairsofspermathecalaperturesaresituatedontheventro-lateral
sidesoftheintersegmentalgrooves,i.e.,5th-9thsegments.
-Asinglefemalegenitalporeispresentinthemid-ventrallineof14th
segment.
-Apairofmalegenitalporesarepresentontheventro-lateralsidesof
the18
th
segment.
-Numerousminuteporescallednephridioporesopenonthesurfaceof
thebody

6. EARTHWORM : Digestive System
ALIMENTARY
CANAL
FEATURES& FUNCTIONS
1.MOUTH Terminal opening in peristomiumoverhung by prostomium
2. BUCCAL
CAVITY
extends from 1
st
to 3
rd
segment
3. PHARYNX Small pear shaped sac from middle of 3
rd
segment to end of 4
th
segment
4. OESOPHAGUSnarrow tubular structure from 5
th
to the 7
th
segment
5. GIZZARD Prominent, oval, hard and thick walled muscular organ in segment 8
th
and 9
th.
It grinds the food with the help of thick muscles and cuticle
6. STOMACH Short narrow and tubular structure from 9
th
to the 14
th
segment. Highly vascular and
glandular walls.
The chalky secretion of the calciferous glands neutralise the humicacid in the humus
7. INTESTINEIntestine starts from the 15th segment onwards and continues till the last segment.
A pair of short and conical intestinal caecaeproject from the intestine on the 26th
segment.
The characteristic feature of the intestine between 26-35 segments is the presence of
internal median fold of dorsal wall called typhlosole. This increases the effective area
of absorption in the intestine.
8. ANUS The alimentary canal opens to the exterior by a small rounded aperture called anus

7. EARTHWORM : Circulatory System
-Pheretimaexhibitsaclosedtypeofbloodvascularsystem,consistingofbloodvessels,capillariesandheart.
Duetoclosedcirculatorysystembloodisconfinedtotheheartandbloodvessels.
-Heart:4pairsoftubularhearts,7
th
and9
th
segment:lateralheartswhereas12
th
and13
th
segment:
lateraloesophagealhearts
-AnteriorLoops:Thinwalled,nonpulsatilelooplikebroadvesselswithoutvalvesin10
th
and11
th
segment
-BloodVessels:Weelorganisedvesselswhichrunalongthebodyofearthworm
i)Dorsalbloodvessel:largestbloodvesselofthebodyrunningmiddorsallyabovethealimentarycanal
fromoneendofthebodytotheother.Ithasvalvesandreceivesbloodfrom
variouspartsofthebody
ii)Ventralbloodvessel:Alsoextendsfromendtoendbutitdoesnothavevalves.Itisthemain
distributingvessel.

8. EARTHWORM : Circulatory System
-BloodGlands:Insegments4
th
,5
th
,and6
th
lyingabovethepharyngealmassaresmallredcolouredfollicular
bodiescalledasbloodglands.Theyproducebloodcorpusclesandhaemoglobin.
-Blood:madeupofcolourlessplasmaandbloodcells.Therespiratorypigment,haemoglobinispresentinthe
plasmaandhelpsintransportofoxygen.Theonlytypeofbloodcellistheleucocyteandhenceisphagocytic
innature.

9. EARTHWORM : Excretory System
NEPHRIDIA FEATURES& FUNCTIONS
1.Pharyngeal three paired tufts in the 4th, 5th and 6
th
segments
2. Integumentaryattached to lining of the body wall of segment 3 to the last that
open on the body surface
3. Septal present on both the sides of intersegmentalsepta of segment
15 to the lastthat open into intestine
-These different types of nephridiaare basically similar in structure
-Nephridiaregulate the volume and composition of the body fluids.
-A nephridiumstarts out as a funnel that collects excess fluid from coelomic
chamber.
-The funnel connects with a tubular part of the nephridiumwhich delivers the
wastes through a pore to the surface in the body wall into the digestive tube.

10. EARTHWORM : Nervous System
Alltheactivitiesoftheearthwormareunderthecontrolofthenervoussystem.
TheNervousSystemismadeupofanAnteriorNerveringandPosteriorNerve
cord
Nervoussystemisbasicallyrepresentedbygangliaarrangedsegmentwiseonthe
ventralpairednervecord.
Nervous SystemFeatures and Functions
Nerve ring &
Nerve cord
-The nerve cord in the anterior region (3rd and 4th
segments) bifurcates, laterally encircling the pharynx and
joins the cerebral ganglia dorsally to form a nerve ring.
-The cerebral ganglia along with other nerves in the ring
integrate sensory input as well as command muscular
responses of the body

11. EARTHWORM : Reproductive System

12. EARTHWORM : Male Reproductive System
FEATURES& FUNCTIONS
Testis sacsTherearetwopairsoftestissacsinthe10thand11thsegments.Eachsac
enclosesatestisandaspermiducalfunnel
Testis -Therearetwopairsoftestesin10thand11thsegments.
-Eachtestisarisesfromtheanteriorwallofeachtestissac.
-Immaturespermatozoaproducedbythetestesfirstentertestissacsand
thenmaketheirwayintoseminalvesiclewheretheyundergofurther
developmenttobecomematuresperms.
Seminal
Vesicle
Therearetwopairsofseminalvesiclesin10thand11thsegments
Spermiducal
funnel
-Therearetwopairsofspermiducalfunnelsonein10thsegmentandthe
otherin11thsegment.
-Eachspermiducalfunnelleadsintoafinetube,thevasdeferens.
Vasa deferentia-Therearepresenttwopairsofvasadeferentia.Eachspermiducalfunnelleads
intoavasadeferens.
-Vasadeferentiaofeachsiderunveryclosetoeachotheruptothe18
th
segment.In18thsegment,boththevasadeferentiaofeachsidearejoinedto
theprostateductcomingfromtheprostategland.
-Twovasadeferentiaductsandoneprostateductofeachsideareenclosedin
acommonthickmuscularsheathcalledthecommonprostateandspermatic
duct.Theyopentotheoutsideseparatelyintomalegenitalaperture.

13. EARTHWORM : Male Reproductive System
FEATURES& FUNCTIONS
Prostate -Apairoflargeprostateglandsarepresentinearthworm.
-Theseglandsaresituatedoneithersideoftheintestineandextendfromthe
16thtothe21stsegment.
-Theyproduceasecretion,whichservesasamediumfortransferofsperms
Accessory
glands
-Therearetwopairsofwhitishglandularmassessituatedinternallyin17th
and19thsegments.
-Thesecretionoftheseglandsissupposedtohelpinkeepingthetwoworms
closetogetherduringcopulation

14. EARTHWORM : Female Reproductive System
FEATURES& FUNCTIONS
Ovaries Thereisapairofwhiteminutemassesoftheovariesattachedtothe
posteriorsurfaceoftheseptumpresentbetweenthe12
th
and13
th
segments.Theyproduceova.
Oviducts -Theyaretwoshorttubeseachlyingimmediatelybehindthe
respectiveovary.
-Thetwoovariantubesconvergetomeetinthebodywallandopen
tooutsidebyafemalegenitalapertureonmid-ventralsideofthe
14
th
segment.
-Thematureovaliberatedbyeachovaryarereceivedbytheoviducts
andarefinallypassedoutsideintothecocoonthroughafemale
genitalaperture
Spermathecae-Therearepresentfourpairsofspermathecaewhichlieinthe6th,
7th8
th
and9
th
segments.
-Theyopentooutsidethroughthespermathecalporessituated
ventro-laterallyinthesuccessivegroovesseparatingtheabove
mentionedsegments.Theystorethespermsreceivedfromanother
earthwormduringcopulation

15. EARTHWORM : Fertilization
-Amutualexchangeofspermoccursbetweentwo
wormsduringmating.
-Onewormhastofindanotherwormandtheymate
juxtaposingoppositegonadalopeningsexchanging
packetsofspermscalledspermatophores.
-Maturespermandeggcellsandnutritivefluidare
depositedincocoonsproducedbytheglandcellsof
clitellum.
-Fertilisationanddevelopmentoccurwithinthe
cocoonswhicharedepositedinsoil.
-Theova(eggs)arefertilisedbythespermcellswithin
thecocoonwhichthenslipsoffthewormandis
depositedinoronthesoil.
-Thecocoonholdsthewormembryos.Afterabout3
weeks,eachcocoonproducestwototwentybaby
wormswithan
averageoffour.
Earthwormsdevelopmentisdirect,i.e.,thereisnolarva
formed.