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
It discusses basic information regarding a hemichordate animal called Balanoglossus or Acorn worm, which is also a good connecting link between the non-chordates and chordates.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
ORIGIN OF CHORDATES
Animal kingdom is basically divided into two sub kingdoms:
Non-chordata- including animals without notochord.
Chordata- This comprising animals having notochord or chorda dorsalis.
Chordates were evolved sometime 500 million years ago during Cambrian period (invertebrates were also began to evolve in this period) .
Chamberlain (1900) pointed out that all modern chordates possess glomerular kidneys that are designed to remove excess water from body.
It is believed that Chordates have originated from invertebrates.
It is difficult to determine from which invertebrate group the chordates were developed.
Chordate ancestors were soft bodied animals. Hence they were not preserved as Fossils.
However, early fossils of chordates have all been recovered from marine sediments and even modern protochordates are all marine forms.
Also glomerular kidneys are also found in some marine forms such as myxinoids and sharks. That makes the marine origin of chordates more believable.
Chordates evolved from some deuterostome ancestor (echinoderms, hemichordates, pogonophorans etc.) as they have similarities in embryonic development, type of coelom and larval stages.
Many theories infers origin of chordates, hemichordates and echinoderms from a common ancestor.
It discusses basic information regarding a hemichordate animal called Balanoglossus or Acorn worm, which is also a good connecting link between the non-chordates and chordates.
Chordata is the last phylum of kingdom Animalia.
Which is further subdivided into subphylums, divisions and classes.
The Slides shows the classification of the phylum along with the basis on which it is classified.
(includes examples along with pictures for easy understanding and memorizing)
ORIGIN OF CHORDATES
Animal kingdom is basically divided into two sub kingdoms:
Non-chordata- including animals without notochord.
Chordata- This comprising animals having notochord or chorda dorsalis.
Chordates were evolved sometime 500 million years ago during Cambrian period (invertebrates were also began to evolve in this period) .
Chamberlain (1900) pointed out that all modern chordates possess glomerular kidneys that are designed to remove excess water from body.
It is believed that Chordates have originated from invertebrates.
It is difficult to determine from which invertebrate group the chordates were developed.
Chordate ancestors were soft bodied animals. Hence they were not preserved as Fossils.
However, early fossils of chordates have all been recovered from marine sediments and even modern protochordates are all marine forms.
Also glomerular kidneys are also found in some marine forms such as myxinoids and sharks. That makes the marine origin of chordates more believable.
Chordates evolved from some deuterostome ancestor (echinoderms, hemichordates, pogonophorans etc.) as they have similarities in embryonic development, type of coelom and larval stages.
Many theories infers origin of chordates, hemichordates and echinoderms from a common ancestor.
Porifera is a phylum of primitive invertebrate animals comprising the sponges and having a cellular grade of construction without true tissue or organ formation but with the body permeated by canals and chambers through which a current of water flows and passes in its course through one or more cavities lined with choanocytes.
Porifera is a phylum of primitive invertebrate animals comprising the sponges and having a cellular grade of construction without true tissue or organ formation but with the body permeated by canals and chambers through which a current of water flows and passes in its course through one or more cavities lined with choanocytes.
Larval forms and their significance in arthropodaRekha Jalandra
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Mollusca general characters and classification
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.
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
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
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
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
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
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’
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
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
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