The document discusses the phylum Mollusca. Some key points: - Mollusca is the second largest phylum and includes animals like snails, slugs, clams, squids and octopuses. - They are soft-bodied and many have an external or internal shell. Their main distinguishing feature is the shell, which has architectural and ornamental value. - The phylum is divided into 7 classes based on shell structure and foot position. These include Gastropoda (snails and slugs), Bivalvia (clams and oysters), and Cephalopoda (squids and octopuses). - Molluscs have

1. Phylum MolluscaPhylum Mollusca
ASHOK KUMAR BOLLAPALLIASHOK KUMAR BOLLAPALLI
M.Sc.,B.Ed.,CSIR-NET,M.A(Lit) .D.C.A.(Ph.D.)M.Sc.,B.Ed.,CSIR-NET,M.A(Lit) .D.C.A.(Ph.D.)
LECTURER IN ZOOLOGYLECTURER IN ZOOLOGY
KRK GOVT DEGREE COLLEGEKRK GOVT DEGREE COLLEGE
ADDANKI-523201ADDANKI-523201
9652929696,94416352649652929696,9441635264
ashokkumarzoology@gmail.comashokkumarzoology@gmail.com

2. Introduction - MolluscaIntroduction - Mollusca
 Second largest phylumSecond largest phylum
 The term “Mollusca” was coined by AristotleThe term “Mollusca” was coined by Aristotle
Mollis=soft(Latin)Mollis=soft(Latin)
 Study of Molluscs is known as MalacologyStudy of Molluscs is known as Malacology
 Study of shells is known as ConchologyStudy of shells is known as Conchology
 The size varies from 0.5mm to some metresThe size varies from 0.5mm to some metres
 Architeuthis-Giant squid=largest invertebrate(6m)Architeuthis-Giant squid=largest invertebrate(6m)
 They are in all habitats except in airThey are in all habitats except in air
 The main character is Shell, which has architecturalThe main character is Shell, which has architectural
and ornamental values.and ornamental values.

3. Generalized Mollusc AnatomyGeneralized Mollusc Anatomy

4. Phylum MolluscaPhylum Mollusca
 Marine , some freshMarine , some fresh
watered and others onwatered and others on
landland
 Bilaterally symmetricalBilaterally symmetrical
but Gastropods arebut Gastropods are
asymmetrical due toasymmetrical due to
torsiontorsion
 Triploblastic EucoelomicTriploblastic Eucoelomic
(Schizocoelomates)(Schizocoelomates)
ProtostomesProtostomes

Tridacna squamosa
Tridacna gigas

5. Phylum MolluscaPhylum Mollusca
 Soft & unsegmented BodiedSoft & unsegmented Bodied
 Shelled(external/internal)Shelled(external/internal)
 Some without(vaginulus)Some without(vaginulus)
 CephalizationCephalization
 Sensory organsSensory organs
 MouthsMouths
 Body DivisionsBody Divisions
 Visceral MassVisceral Mass
 Head-FootHead-Foot
 MantleMantle
Tonicella lineata

6. Shell Structure & FormationShell Structure & Formation

7. Phylum MolluscaPhylum Mollusca
 Mantle – thin fleshy fold of skin(pallial layer)Mantle – thin fleshy fold of skin(pallial layer)
 The space between Mantle and Body parts-The space between Mantle and Body parts-
Mantle/Pallial cavityMantle/Pallial cavity
 Foot is ventral-thick muscular structure forFoot is ventral-thick muscular structure for
locomotion but modified to perform swimming,locomotion but modified to perform swimming,
creeping or burrowingcreeping or burrowing
 Unstriped muscles form BodyUnstriped muscles form Body
 Respiratory organs are gills/ctenidia vary form oneRespiratory organs are gills/ctenidia vary form one
to many pairs. Lung developed in terrestrial forto many pairs. Lung developed in terrestrial for
aerial respiration.aerial respiration.
 Olfactory organ-osphradium is presentOlfactory organ-osphradium is present

8. Respiration: GillsRespiration: Gills

9. Phylum MolluscaPhylum Mollusca
 Complete digestive tractComplete digestive tract
 Radula-rasping organRadula-rasping organ
 Digestive glands-Hepatopancreas, Salivary glandsDigestive glands-Hepatopancreas, Salivary glands
 Specialized feeding structuresSpecialized feeding structures
 Circulatory systemCirculatory system
 Heart (1-4 auricles and a ventricle)Heart (1-4 auricles and a ventricle)
 Open system in most groupsOpen system in most groups
 Blood contains Haemocyanin.Blood contains Haemocyanin.
 Closed in cephalopodsClosed in cephalopods
 Coelom restricted to pericardium in most casesCoelom restricted to pericardium in most cases
 Excretory system:Kidney-like nephridia(1-6 pairs)Excretory system:Kidney-like nephridia(1-6 pairs)
Octopus briareus

10. Gastropod FeedingGastropod Feeding
ApparatusApparatus

11. Phylum MolluscaPhylum Mollusca
 Advanced nervousAdvanced nervous
systemsystem
 Brain,Brain,
 Paired cerebral, pedal,Paired cerebral, pedal,
pleural and visceralpleural and visceral
gangliaganglia
 connectives,commisuresconnectives,commisures
 Sensory organsSensory organs
Eyes(simple and camera)Eyes(simple and camera)
Sensorypapillae,statocystSensorypapillae,statocyst
OspradiaOspradia

12. Phylum MolluscaPhylum Mollusca
 ReproductionReproduction
 Monoecious and dioeciousMonoecious and dioecious
 External & internal fertilizationExternal & internal fertilization
 Cleavage is determinate and spiralCleavage is determinate and spiral
 Development is direct/ indirect with Trochopore orDevelopment is direct/ indirect with Trochopore or
Veliger larvaeVeliger larvae

13. Classification of MolluscaClassification of Mollusca
 Based on the structure and shape of the shellBased on the structure and shape of the shell
and the position of footand the position of foot
 It is divided into seven classes- they areIt is divided into seven classes- they are
 AplacophoraAplacophora
 Mono placophoraMono placophora
 Poly placophoraPoly placophora
 ScaphopodaScaphopoda
 GastropodaGastropoda
 PelecypodaPelecypoda
 CephalopodaCephalopoda

14. 1.Class : APLACOPHORA1.Class : APLACOPHORA
 Solenogasters which are primitive like wormsSolenogasters which are primitive like worms
 Marine, live in burrows, some live among coralsMarine, live in burrows, some live among corals
 Shell absent-hence the nameShell absent-hence the name
 Foot is not prominent-either vestigial or absentFoot is not prominent-either vestigial or absent
 Body is covered by thick mantle provided withBody is covered by thick mantle provided with
calcareous spiculescalcareous spicules
 Alimentary canal is tubular, radula, digestion-Alimentary canal is tubular, radula, digestion-
extracellular and intracellularextracellular and intracellular
 Respiration – Gills/Mantle as in NeomeniaRespiration – Gills/Mantle as in Neomenia

15. 1.Class : APLACOPHORA1.Class : APLACOPHORA
 Monoecious/dioeciousMonoecious/dioecious
 Single/ paired gonads are presentSingle/ paired gonads are present
 In some nephridial ducts at the posterior end unite toIn some nephridial ducts at the posterior end unite to
form a copulatory organform a copulatory organ
 Development is indirect with trochophore larvaDevelopment is indirect with trochophore larva
 It includes two orders.It includes two orders.
Sl
.No
Name of the ORDER EXAMPLES
1 Chaetodermomorpha Chaetoderma
2 Neomeniomorpha Neomenia,Proneom
enia

16. 2.Class : MONOPLACOPHORA2.Class : MONOPLACOPHORA
 Mostly extinct- Cambrian & DevonianMostly extinct- Cambrian & Devonian
 In 1952 Neopilina galathea was found(GalatheaIn 1952 Neopilina galathea was found(Galathea
expedition).Later 3 more genera addedexpedition).Later 3 more genera added
 Body oval and bilaterally symmetricalBody oval and bilaterally symmetrical
 Shell is present on dorsal side as a single pieceShell is present on dorsal side as a single piece
 Head is not distinct. Eyes are absentHead is not distinct. Eyes are absent
 Ciliated tentacles near mouthCiliated tentacles near mouth
 Flat foot on ventral sideFlat foot on ventral side
 5-6 pairs of unipectinate gills5-6 pairs of unipectinate gills
 Have spacious coelom- uniqueHave spacious coelom- unique

17. 2.Class : MONOPLACOPHORA2.Class : MONOPLACOPHORA
 Radula and sub-radula are presentRadula and sub-radula are present
 Crystalline style in stomach. Intestine is spirallyCrystalline style in stomach. Intestine is spirally
coiled. Paired digestive glands are presentcoiled. Paired digestive glands are present
 Paired pericardial sinus surrounds the heart.Paired pericardial sinus surrounds the heart.
Heart is made of 2 pairs of auricles and a pair ofHeart is made of 2 pairs of auricles and a pair of
ventriclesventricles
 Excretion – 6 pairs of nephridiaExcretion – 6 pairs of nephridia
 Dioecious , two pairs of testes below theDioecious , two pairs of testes below the
intestineintestine
 Example : NeopilinaExample : Neopilina

18. 3.Class : Polyplacophora3.Class : Polyplacophora
 Chitons – dorsoventrally flattened oval/ellipticalChitons – dorsoventrally flattened oval/elliptical
 Marine, live in intertidal zoneMarine, live in intertidal zone
 Head is separated from foot by a narrow grooveHead is separated from foot by a narrow groove
 Eyes and tentacles are absentEyes and tentacles are absent
 Large muscular foot on ventral sideLarge muscular foot on ventral side
 Shell is on mid- dorsal region with eight broad platesShell is on mid- dorsal region with eight broad plates
 Mantle is in the form of a girdle. It bears scales/spinesMantle is in the form of a girdle. It bears scales/spines

19. Polyplacophoran AnatomyPolyplacophoran Anatomy

20. 3.Class : Polyplacophora3.Class : Polyplacophora
 Radula and sub-radula are present. Radula bearsRadula and sub-radula are present. Radula bears
teeth and sub radula tests nature of food.teeth and sub radula tests nature of food.
Salivary and other digestive glands are present.Salivary and other digestive glands are present.
 1-20 pairs of gills in the pallial groove1-20 pairs of gills in the pallial groove
 Dioecious with single gonad.Dioecious with single gonad.
 Trochophore in life cycle.Trochophore in life cycle.
Sl .No Name of the ORDER EXAMPLES
1 Lepidopleurida Lepidopleurus
2 Chitonida Chiton

21. Chiton tuberculatusChiton tuberculatus lives in the rocky intertidal zoneslives in the rocky intertidal zones
eat algae with its radula..8 shell plateseat algae with its radula..8 shell plates

22. 4.Class : Scaphopoda4.Class : Scaphopoda
 Burrowing animalsBurrowing animals
 commonly called as Tusk/Tooth shells,commonly called as Tusk/Tooth shells,
 shell is tubular and open at both endsshell is tubular and open at both ends
 Head is not distinct and eyes are absentHead is not distinct and eyes are absent
 Foot is boat shaped and pointed, muscular helpsFoot is boat shaped and pointed, muscular helps
in burrowingin burrowing
 Mantle surrounds the body on all sides toMantle surrounds the body on all sides to
become tubular and opens at both endsbecome tubular and opens at both ends
 Gills absent. Mantle folds help in respirationGills absent. Mantle folds help in respiration

23. 4.Class : Scaphopoda4.Class : Scaphopoda
 Circulatory system is simple. Heart isCirculatory system is simple. Heart is
rudimentary. Pericardial sinus is absentrudimentary. Pericardial sinus is absent
 Excretion is by a pair of nephridiaExcretion is by a pair of nephridia
 Sexes are separate , sexual dimorphism is absent,Sexes are separate , sexual dimorphism is absent,
only one gonad is presentonly one gonad is present
 Life history includes Trochophore and VeligerLife history includes Trochophore and Veliger
larvae.larvae.
 Examples: Dentalium, SiphonodentaliumExamples: Dentalium, Siphonodentalium

24. 5.Class :Gastropoda5.Class :Gastropoda
 Inactive and sluggish animals (snails and slugs)Inactive and sluggish animals (snails and slugs)
 Head is distinct. Foot and visceral mass alsoHead is distinct. Foot and visceral mass also
presentpresent
 Bilaterally symmetrical. Due to Torsion theyBilaterally symmetrical. Due to Torsion they
become asymmetricalbecome asymmetrical
 Head bears two pairs of tentacles and a pair ofHead bears two pairs of tentacles and a pair of
stalked eyesstalked eyes
 Foot is ventral. It is a flat muscular organFoot is ventral. It is a flat muscular organ
modified for swimming and burrowingmodified for swimming and burrowing
 Respiration by ctenidia, lungs or bothRespiration by ctenidia, lungs or both

25. Generalized Gastropod AnatomyGeneralized Gastropod Anatomy

26. 5.Class :Gastropoda5.Class :Gastropoda
 Heart is with two auricles and a ventricle.Heart is with two auricles and a ventricle.
Pericardial space surrounds it.Pericardial space surrounds it.
Haemocyanin/haemoglobin-blood pigmentHaemocyanin/haemoglobin-blood pigment
 One or two pairs of kidneys for excretionOne or two pairs of kidneys for excretion
 Well developed Nervous system, nerves in theWell developed Nervous system, nerves in the
shape of ‘8’ due to torsion- such N.S. is calledshape of ‘8’ due to torsion- such N.S. is called
‘streptoneury/chaistoneury’. In some it is not in‘streptoneury/chaistoneury’. In some it is not in
this shape due to detorsion. Such N.S. is calledthis shape due to detorsion. Such N.S. is called
‘Euthyneury’‘Euthyneury’

27. Class Gastropoda - TorsionClass Gastropoda - Torsion

28. 5.Class :Gastropoda5.Class :Gastropoda
 Unisexual or hermaphrodites. Only one gonad nearUnisexual or hermaphrodites. Only one gonad near
hepatopancreashepatopancreas
 Trochophore or Veliger larva in life historyTrochophore or Veliger larva in life history
 GASTROPODA is divided into three sub-classesGASTROPODA is divided into three sub-classes
Sl.N
o
Sub-Class Examples
1 Prosobranchiata Patella, Pila, Cyprea, Nerita
2 Opisthobranchiata Aplysia ,Doris,
Pteropod,Eolis, Limacina
3 Pulmonata Lymnaea, Planorbis, Helix,
Limax

29. Trochophore LarvaTrochophore Larva

30. Mollusc TaxonomyMollusc Taxonomy
GastropodaGastropoda
Prosobranchia(streptoneura)Prosobranchia(streptoneura)
 Shelled marine gastropods eg: Murex , Cypraea,Shelled marine gastropods eg: Murex , Cypraea,
Patella, HeliotisPatella, Heliotis
Atlantic triton’s trumpetAtlantic triton’s trumpet
((Charonia variegataCharonia variegata)) Tiger cowrie (Tiger cowrie (Cypraea tigrisCypraea tigris))

31. GastropodaGastropoda--
OpisthobranchiaOpisthobranchia
(Euthyneury)(Euthyneury)Sea slugsSea slugs
(marine)(marine)
Eg:Aplysia,Limacina,Pteropods,Eg:Aplysia,Limacina,Pteropods,
Doris,Berthelinia,OnchidiumDoris,Berthelinia,Onchidium
zebra sea goddesszebra sea goddess
((Hypselodoris zebraHypselodoris zebra))
Spotted sea hare (Spotted sea hare (Aplysia dactylomelaAplysia dactylomela))
Phidiana hiltoni

32. Mollusc TaxonomyMollusc Taxonomy
GastropodaGastropoda
PulmonataPulmonata
Terrestrial snails/slugsTerrestrial snails/slugs
FreshwaterFreshwater
snailssnails
Eg: Helix, LimaxEg: Helix, Limax
Lymnaea,Lymnaea,
PlanorbisPlanorbis
Helminthoglypta walkeriana
Giant banana slug
(Ariolimax columbians)

33. Terrestrial GastropodsTerrestrial Gastropods
- Pulmonata- Pulmonata
 The mantle cavity servesThe mantle cavity serves
as a “lung”as a “lung”
 Glandular epidermisGlandular epidermis
 Secrete mucus (slime)Secrete mucus (slime)
upon which gastropodupon which gastropod
glidesglides

34. Terrestrial Gastropod -Terrestrial Gastropod -
PulmonataPulmonata
 Slugs lackSlugs lack
shellsshells
 Mantle thickenedMantle thickened
 PneumostomePneumostome
 Air intake into mantle cavityAir intake into mantle cavity
PneumostomePneumostome

35. Gastropod Veliger LarvaGastropod Veliger Larva
Velia
Mouth
Shell

36. 6. Class: Pelecypoda6. Class: Pelecypoda
 Bivalves because of shell with two halves joined withBivalves because of shell with two halves joined with
hinge teeth. Body is laterally compressedhinge teeth. Body is laterally compressed
 Head is distinct. Eyes and tentacles absent. But labialHead is distinct. Eyes and tentacles absent. But labial
palps are present near the mouth which help inpalps are present near the mouth which help in
feeding.feeding.
 Foot is flat and is in the form of axe which helps inFoot is flat and is in the form of axe which helps in
the movement at the bottom of water. In some byssusthe movement at the bottom of water. In some byssus
apparatus helps to adhere to substratumapparatus helps to adhere to substratum
 Muscles are well developed. The two halves of theMuscles are well developed. The two halves of the
shell open and close by contractions and relaxations ofshell open and close by contractions and relaxations of
two adductor muscles.two adductor muscles.

37. 6. Class: Pelecypoda6. Class: Pelecypoda
 Mantle covers the body on dorsal and lateral sides.Mantle covers the body on dorsal and lateral sides.
At posterior end the mantle forms two siphonsAt posterior end the mantle forms two siphons
called inhalant siphon & exhalent siphoncalled inhalant siphon & exhalent siphon
 Respiration- a pair of lamellar ctenidia projectingRespiration- a pair of lamellar ctenidia projecting
ventrally into mantle cavityventrally into mantle cavity
 Buccal mass is without radula, subradula andBuccal mass is without radula, subradula and
odontophore. Alimentary canal is a coiled tube withodontophore. Alimentary canal is a coiled tube with
crystalline style in the intestinecrystalline style in the intestine
 These are ciliary feedersThese are ciliary feeders
 Kidneys are simple and glandularKidneys are simple and glandular

38. 6. Class: Pelecypoda6. Class: Pelecypoda
 Blood contains corpuscles and haemocyanin asBlood contains corpuscles and haemocyanin as
pigment. A single aorta arises from the anteriorpigment. A single aorta arises from the anterior
part of the heart which is made of two auriclespart of the heart which is made of two auricles
and a ventricle surround by pericardium.and a ventricle surround by pericardium.
 Cerebral, Pedal and pleural ganglia are seen inCerebral, Pedal and pleural ganglia are seen in
nervous system. Sense organs are located on thenervous system. Sense organs are located on the
margin of mantle foldsmargin of mantle folds
 Sexes are separate. Some hermophodites. SingleSexes are separate. Some hermophodites. Single
pair of gonads are present. Gonoducts open intopair of gonads are present. Gonoducts open into
mantle cavitymantle cavity

39. 6. Class: Pelecypoda6. Class: Pelecypoda
 Life history includes trochophore and veligerLife history includes trochophore and veliger
larvae. Glochidium is a modified veliger andlarvae. Glochidium is a modified veliger and
parasitic on fishes is seen in fresh water mussels.parasitic on fishes is seen in fresh water mussels.
 Pelecypoda is divided into three sub classes.Pelecypoda is divided into three sub classes.
Sl
.No
Sub-class Exmples
1 Protobranchiata Necula, Yoldia
2 Lamellibranchiata Pinctada,Mytilus, Unio, Teredo, Pecten
3 Septibranchiata Poromya,Cuspidaria

40. BivalviaBivalvia
 Clams, oysters,Clams, oysters,
mussels, scallopsmussels, scallops
Bay scallop (Aequipecten irradians)
Edible mussels
(Mytilus edulis)
Ostrea edulis

41. A Pearl Among the SwineA Pearl Among the Swine

42. Phylum Mollusca, Class BilvaliaPhylum Mollusca, Class Bilvalia
 Two shellsTwo shells
 Incurrent & excurrent siphonsIncurrent & excurrent siphons
 No cephalizationNo cephalization

43. Generalized Bivalve AnatomyGeneralized Bivalve Anatomy

44. Generalized Bivalve AnatomyGeneralized Bivalve Anatomy
(XS)(XS)

45. Bivalve Anatomy (Sagittal)Bivalve Anatomy (Sagittal)

46. Bivalves are Typically Filter FeedersBivalves are Typically Filter Feeders

47. Bivalve Life CycleBivalve Life Cycle

48. Glochidia – Unique Larval Stage ofGlochidia – Unique Larval Stage of
Freshwater BivalvesFreshwater Bivalves
 Internal fertilizationInternal fertilization
 Early development in broodEarly development in brood
chamber (region of mantlechamber (region of mantle
cavity)cavity)
 Release of glochidia veligerRelease of glochidia veliger
larvaelarvae
 Glochidia attach to gills ofGlochidia attach to gills of
fish and are distributedfish and are distributed

49. 7.Class : Cephalopoda7.Class : Cephalopoda
 Bilaterally symmetrical, exclusively marineBilaterally symmetrical, exclusively marine
 Active free swimmingActive free swimming
 Body is divisible into head and trunk. Head isBody is divisible into head and trunk. Head is
distinct and bears a pair of well developed eyesdistinct and bears a pair of well developed eyes
 Head is bearing 8-10 arms around mouth, whichHead is bearing 8-10 arms around mouth, which
bears suckersbears suckers
 Visceral mass is uncoiled and covered on allVisceral mass is uncoiled and covered on all
sides by mantle.sides by mantle.
 Mantle encloses pallial cavity in which gills areMantle encloses pallial cavity in which gills are
locatedlocated

50. 7.Class : Cephalopoda7.Class : Cephalopoda
 Shell is internal (Sepia), external (Nautilus) orShell is internal (Sepia), external (Nautilus) or
absent (Octopus)absent (Octopus)
 Foot is modified into arms around mouth and aFoot is modified into arms around mouth and a
funnel or siphone through which water isfunnel or siphone through which water is
pumped out from pallial cavitypumped out from pallial cavity
 Radula and a pair of jaws are present in buccalRadula and a pair of jaws are present in buccal
cavitycavity
 Two pairs of salivary glands and other glandsTwo pairs of salivary glands and other glands
 Closed blood vascular systemClosed blood vascular system

51. 7.Class : Cephalopoda7.Class : Cephalopoda
 Kidneys and ctenidia are one or two pairsKidneys and ctenidia are one or two pairs
 Sexes are separate . Gonad is single.Sexes are separate . Gonad is single.
 In males one pair of arms is modified to form aIn males one pair of arms is modified to form a
copulatory organ( Hectacotylized)copulatory organ( Hectacotylized)
 Developemnt is directDevelopemnt is direct
Sl.No Sub-Class Examples
1 Ammonoidea Ammonites,Goniatites
2 Nautiloidea Nautilus
3 Coeleoidea Sepia , Loligo, Octopus

52. Cephalopod AnatomyCephalopod Anatomy

53.  CephalopodaCephalopoda
 Octopus, squid, nautilusOctopus, squid, nautilus
Giant cuttlefish (Giant cuttlefish (Sepia latimanusSepia latimanus))
Nautilus sp
Octopus sp

54. Squid are the largestSquid are the largest
CephalopodsCephalopods

55. Nautilus AnatomyNautilus Anatomy

56. Cephalopod EyeCephalopod Eye

57. Color & Morphology Changes forColor & Morphology Changes for
CamouflageCamouflage