This document summarizes key characteristics of the phylum Mollusca. It describes the 9 main classes of molluscs: Gastropoda, Bivalvia, Cephalopoda, Scaphopoda, Monoplacophora, Polyplacophora, Aplacophora. The classes vary in body structure, shell morphology, habitat, locomotion and other traits. Molluscs display a range of ecologically and economically important roles including as human food sources, sources of pearls, and intermediate hosts of parasites.

3. 3
cuttlefish Nautilus Giant squid Architeuthi
clam
chiton
snail
slug
octopus
scallop

5. CHARACTERISTICS
Second largest phylum in the animal
kingdom (80000 living species and 40000
fossil species)
Soft bodied animals
Body: head, foot and visceral hump
Microscopic to macroscopic
They include chitons, snails, slugs, clams,
oysters, cuttlefish, squids, octopods,
scaphopods, …….
Slow to active organisms
Coelomate, triploplastic, unsegmented

6. Terrestrial, freshwater, or marine
environments
Occur in a wide variety of environments
Have different modes of nutrition
Bilateral symmetry, torsion and coiling in
gastropods
True coelom is reduced
Skin is soft and often secrets the exoskeleton or
the shell
Respiration by one to many gills (ctenidia)
Radula in most molluscs
Circulatory system of open type (except
cephalopods)

7. Blood contains haemocyanin and amoebocytes
The nervous system is composed of a nerve
ring around the oesophagus and two pairs of
nerve cords
Sense organs include tentacles, eye spots,
statocysts in foot and osphradia beside gills
Excretion by a pair of u- shaped metanephridia
Molluscs are unisexual (dioecious) but some
are hermaphrodite (monoecious)
Fertilization is mostly external and rarely
internal
Development is direct (no larva) or indirect
through free swimming trochophore and/or
veliger larvae

8. Economic importance of Mollusca
Human food
Pearls
Buttons
Decoration
Ship-worms
Intermediate hosts of some
parasites

9. 9
Scallops
 coarsely ribbed
 food

10. 10
 Destructive
 Burrow into wood
Shipworms

11. The soft edible parts of the
molluscs represent an important
source of animal protein
The shells are used to manufacture
beautiful gifts or to decorate the
furniture

12. 12
Characteristics of Phylum Mollusca
 All organ systems are present, well-
developed
– Respiratory organs
– Circulatory system, with heart
 Greater body size possible
Freshwater clamSquid

13. GENERAL BODY PLAN
Head
Ventrally located muscular foot
Dorsally located visceral mass
Mantle / pallium – for shell/spicule
secretion
Radula (except for bivalves)
Complete digestive tract
Gonads in visceral mass
Monoecious or dioecious

14. 14
Molluscan body form
2-part body plan:
1. Head-foot
2. Visceral mass
Octopus

15. 15
Mollusk Body Plan

16. 16
Head-foot
Foot:
 ventral
 Muscular structure
 Locomotion
 Attachment
 modifications
Octopus
http://acolyte.org/images/octopus.png

17. 17
Head-foot
Snail radula
Head:
– anterior
– Cephalic sensory organs
– Feeding organs:
Radula
– Most molluscs (not
bivalves)
– rasping structure
– Tongue-like
– Rows backward-
pointing “teeth”
– Scraping food
– drilling

18. 18
Visceral mass
 Digestive organs
 Reproductive
organs
 Circulatory organs
 Respiratory organs
Mantle
 Attached to
visceral mass
 Dorsal skin folds
 protective
 In some, mantle
secretes protective
shell over visceral
mass
Chiton

19. 19
Mantle cavity
– Space between
mantle and foot
– Opens to outside
– Functions:
 Gas exchange
(respiration)
 Excretion/elimination
 Release reproductive
products

20.  Subphylum Conchifera: with 1 shell; (-)
spicules
1. Class Gastropoda
2. Class Bivalvia
3. Class Cephalopoda
4. Class Scaphopoda
5. Class Monoplacophora
 Subphylum Aculifera: with multiple shell
plates; (+) spicules
1. Class Polyplacophora
2. Class Aplacophora
CLASSIFICATION

21. Class Monoplacophora
Bilaterally symmetrical
Have a dorsal, single, dome- or
cap-shaped shell
Has a broad, flattened foot
Includes many fossil species

22. Neopilina
Subphylum Conchifera;
Class Monoplacophora
N. galatheae

23. Class Aplacophora
Worm-like molluscs called
SOLENOGASTERS
With oblong, cylindrical to vermiform
bodies
No shell
Lack a well-defined head
Radula and jaws sometimes present

24. Neomenia
Subphylum Aculifera;
Class Aplacophora
N. yamamotoi

25. Chaetoderma
Subphylum Aculifera;
Class Aplacophora
C. japonicum

26. 26
Classes of Mollusc
Chiton
Class Polyplacophora
“many plate-
bearers”
Chitons
Dorsoventrally
flattened
Shell= 8
overlapping dorsal
plates
marine
Underside of chiton

27. Class Polyplacophora
Include marine chitons
Bodies elongated and dorsoventrally
flattened
Shell divided into:
– 7 or 8 overlapping plates
– Flat, creeping foot
Head reduced
No eyes
Well defined mouth with radula

28. Chiton
Subphylum Aculifera;
Class Polyplacophora
C. glaucus
8 calcareous plates
girdle

29. Acanthozostera
Subphylum Aculifera;
Class Polyplacophora
A. gemmata

30. Class Gastropoda
Members usually
sluggish and sedentary
Mostly with
asymmetrical bodies
Most with single,
conical and spiral shell
May be reduced or
absent (e.g. nudibranch)
(+) Cephalic tentacles
Simple eyes
Radula
Jaws
Large, prominent foot
eyespots
tentacles
jaws

31. RADULA
toothed chitinous
ribbon in the mouth
of most molluscs
used for cutting
and chewing food
before it enters the
esophagus
It is present in all
molluscs except
bivalves

32. 32
Class Gastropoda
 Well-developed sense organs
– Eyes at base or at end of tentacles

33. Major Changes from Generalized Mollusc
 Development of head
 Dorsoventral elongation
 Shell – from shield to retreat
 Torsion
 Conispiral coiling and asymmetry

34. 34
Class Gastropoda
 May have protective shell

35. Torsion
Weight of shell over head, mantle
cavity posterior
Torsion – 180o counterclockwise
rotation of visceral mass, shell,
mantle, mantle cavity
Occurs in larvae not adult
First gastropods
Detorsion

36. Costs of Conispiral Shell
Loss of a gill, nephridium, atrium
Mantle cavity (anus and
nephridiopore) now anterior and
near mouth
Compensation - changes in water
flow or shell structure

37. 37
Coiling
– Absent in some
– Visceral mass/mantle may be
coiled
– Successive coils- whorls
– Caused pressure on right side 
adaptation: loss of rt. kidney,
auricle, gill
 Water enters via left,
leaves right

38. Locomotion
Most move using foot
Most have ciliated sole and
secretory glands (mucus
producing)
Hard-bottom dwelling and
terrestrial, and large soft-bottom
snails - undulating wave of muscle
contractions

39. Feeding
Most often thought of as algal
scrapers (radula)
Deposit feeders
Suspension feeders
Scavengers
Predators
Parasites

41. Turbo (turban snail)
Subphylum Conchifera;
Class Gastropoda
•Torsion
•Whorl
•Spire

42. Cypraea (cowries)
Subphylum Conchifera;
Class Gastropoda
Shell uncoiled

43. Nudibranch
soft-bodied snails
Spanish shawl
Sea slug
rhinophores
gills

44. Class Bivalvia
Oysters, clams, mussels ~8,000 species
(1,300 freshwater, rest marine)
Benthic filter-feeders (a few exceptions)
• No radula
• Enlarged gills
Compressed body
Shell
 Two valves
 Hinged dorsally
 Completely encloses body

45. Class Bivalvia / Pelecypoda
Shells have 2 lateral valves
Elastic ligament
Body is enclosed by a 2-lobed mantle
(elevation)

46. Class Bivalvia / Pelecypoda
hatchet shaped foot in burrowers
Head lacks eyes, radula and tentacles
Freshwater clam

50. 50
Class Bivalvia
 clams, oysters, mussels, scallops
 soft body between two halves of a hinged shell
California musselGiant clam

51. 51
Class Bivalvia
 Aquatic
– most marine, some
fresh water
 no tentacles, head,
radula
 adductor muscle
 Large cilia-covered
gills (in most)

52. 52
Bivalve shell morphology
Umbo- oldest part of shell
– Growth in concentric lines around it

53. 53
 Valves open by adductor muscle
– contraction= closed
– relaxing= open
 Hinge= mantle secretion of more
protein, less calcium carbonate

54. 54
Water movement through bivalves
1. incurrent siphon - water into the mantle
cavity
2. water circulates over
the gills
– Gas exchange
– Filter feeding

55. 55
Locomotion
 Mostly sedentary/sessile
 highly developed muscular foot
– often to burrow into sediment
– move by slicing-like motion of foot
– swim by chattering motion of shell (scallops)

56. 56
Oyster
 lower valve is
cemented to any
object available
 Improve water quality
 Decrease bank erosion
 food
http://www.csc.noaa.gov/scoysters/images/bio/oysters2.jpg

57. 57
Pearl Production
Developing pearl
Epithelium
Shell
 protective function
– foreign substance
between mantle & shell
 mantle secretes pearly layers
of nacre around substance

58. 58
Giant Clam & Burrowing Clam
 some= food
Giant clam
Siphon
Burrowing clam

59. Tridacna (giant clam) -
Subphylum Conchifera;
Class Bivalvia

60. Spondylus (scallop)
Subphylum Conchifera;
Class Bivalvia
S. versicolor
S. princeps

61. Chlamys (scallop)
Subphylum Conchifera;
Class Bivalvia
C. islandicus
C. swifti

62. Perna (mussel)
Subphylum Conchifera;
Class Bivalvia
P. veridis

63. Crassostrea (oyster)
Subphylum Conchifera;
Class Bivalvia
Pacific oysters
Atlantic oyster

64. Anodonta (freshwater clam) –
Subphylum Conchifera;
Class Bivalvia
A. suborbiculata A. anatina

65. Class Cephalopoda
Free-swimming
Fast moving
Active carnivores
Elongated body
Skeleton may be
external, internal or
absent
Foot developed into prehensile arms or
tentacles
Octopus arm

66. Class Cephalopoda
Well-defined head
Complex eyes
Brain in
cartilaginous
cranium
(+) radula
Beak-like jaws
Tentacles
surrounding mouth

67. 67
Class Cephalopoda
 squid, octopus, nautilus, cuttlefish
ammonoids
 “head foot”
 Largest, most complex invertebrates

68. 68
 most highly developed mollusc
– Most active and intelligent
 Marine predator
– carnivorous
Cuttlefish
Cuttlefish camouflage

69. 69
 shell reduced/absent & internalized
(vestigal) (squid, octopus)
 Nautilus- shell
 Cuttlefish- small, enclosed by mantle
Octopus

70. 70
 head is well developed - large eyes
– Complex eyes (except Nautilus)
 Cornea, lens, chambers, retina, iris
 Well-developed nervous system - complex
brain
Squid

71. 71
 foot is modified into multiple tentacles
with suckers (in some)
– Grasp prey
– Taste via suckers
– Crawling
 siphon forces out water: “jet propulsion”
 Octopus movement

72. 72
 squid & octopus possess ink gland which
produce melanin ; escape

73. 73
Octopus
 Eight arms with suckers
 Crawl or eject water from siphon
 Change skin color
 Most intelligent invertebrate
– Colorblind, but can be taught different
shapes

74. 74
Octopus
 camouflage
http://www.cephbase.utmb.edu/viddb/vidsrch3.cfm?ID=132&CephID=495

75. 75
 Some octopi can kill humans:
– Blue-ringed octopus
 Size of golf ball
 Bacteria in salivary glands
 Paralysis, but victim fully conscious
Blue-ringed octopus

76. 76
Nautilus
 Up to 94 tentacles
– No suckers
 Shell with many gas
chambers
Nautilus

77. 77
Ammonoids
 Extinct
– 400 to 65 MYA
 Died out with
dinosaurs

78. Loligo (squid)
Subphylum Conchifera;
Class Cephalopoda
8 arms and 2 tentacles
mantle
siphon
ctenidia

79. Sepia (cuttlefish)
Class Cephalopoda

80. Octopus (octopus) –
Subphylum Conchifera;
Class Cephalopoda

81. Nautilus (nautiloid) –
Subphylum Conchifera;
Class Cephalopoda

82. 82
Circulatory system of molluscs
 Open circulatory system (except Class
Cephalopoda)
– Open circulatory system
 heart pumps hemolymph (blood) through body
cavity, b/w cells
 No small blood vessels

83. 83
Circulatory system of molluscs
– Closed circulatory system (Class
Cephalopoda)
 Blood confined to vessels

85. 85
Molluscan reproduction
 Mostly dioecious
http://www.biology.ualberta.ca/courses.hp/zool250/Labs/Lab08/Lab08.htm
Long-finned squid-
Loligo
Giant squid

87. Class Scaphopoda
Burrowing and sedentary
Shell in one piece
Shell opens on both sides
With modified conical foot
Head is reduced or absent
No eyes
With radula, jaws and thin tentacles

88. Dentalium (Elephant’s tusk shell)
Subphylum Conchifera;
Class Scaphopoda
shell
anterior
posterior

89. 89
Class Scaphopoda
– Tooth shells
– Long, slender body
– Burrows into mud
– Shell open at both ends
http://www.ucmp.berkeley.edu/mollusca/scaphs/scaphopoda.html

90. Digestive system of mollusca

91. Nervous system of mollusca

94. Class: Cephalopoda
It is a very diverse class, with 600 living species
and more than 7500 fossil species.
The class, Cephalopoda, includes the
Chambered Nautilus, cuttlefish, squid, and
octopus, as well as fossil ammonite and other fossil
forms.
Size varies from planktonic to some as large as
sixty feet; e.g., the present day squid, Architeuthis
princeps, found in open ocean.
 However, most cephalopods are small, and they
form a major component of the food web of larger
fish and whales.

96. Dibranchiata Tetrabranchiata
e.g. Octopus, Sepia e.g. Nautilus
One pair of gills Two pairs of gills
One pair of kidneys Two pairs of kidneys
One pair of auricles Two pairs of auricles
The shell is internal or absent External large, thin, coiled shell
The arms are 8 to 10 arms,
bearing suckers
Numerous tentacles without
suckers
The funnel is simple and forms
a complete tube
The funnel is formed of 2 lobes
(not simple)

97. Order: Decapoda Order: Octopoda
e.g. Sepia, Loligo e.g. Octopus
Shell is internal Shell is absent
The body is elongated The body is globular
Has a pair of lateral fins Has no fins
8 arms and 2 long tentacles 8 arms
Arms provided with stalked
suckers
Arms provided with sessile
suckers

98.  Echinoderms are a phylum of marine animals
including the sea star and the sand dollar.
 Echinoderms are found at every ocean depth,
from the intertidal zone to the abyssal zone.
 The phylum contains about 7,000 living
species.
 The Echinoderms are important both
biologically and geologically.
Phylum: Echinodermata

99.  Echinoderms form a well-defined and highly-derived
clade of metazoans.
 They have attracted much attention due to their
extensive fossil record, ecological importance in the
marine realm, intriguing adult morphology, unusual
biomechanical properties, and experimentally
manipulable embryos.
 The approximately 7,000 species of extant
echinoderms fall into five well-defined clades:
Crinoidea (sea lilies and feather stars), Ophiuroidea
(basket stars and brittle stars), Asteroidea (starfishes),
Echinoidea (sea urchins, sand dollars, and sea
biscuits), and Holothuroidea (sea cucumbers).
 Approximately 13,000 echinoderm species are known
from the fossil record.
Introduction

100. Economic importance
 Most humans know the Echinoderms rather from the
unpleasant side: if one finds oneself near the coast, on a
rocky shore or reef, one must beware the prick of a sea
urchin.
 However in the kitchens of some countries,echinoderms
are regarded as a delicacy; and for children sea-urchin
skeletons are as popular a collecting object as brightly
coloured starfish are fascinating.
 Around 50,000 tons of sea urchins are captured each
year, the gonads of which are consumed particularly in
Japan, Peru and in France. Sea cucumbers are also
considered a delicacy in some countries of south east Asia.
 It does appear that some sea cucumber toxins restrain the
growth rate of tumour cells.
 The calcareous tests or shells of echinoderms are used as
a source of lime by farmers in areas where limestone is
unavailable.

101. 1. Five fold symmetry: arms or rays occurs in multiple of
5's.
2. Advanced Biological systems:
--Digestive system including mouth, alimentary
canal (intestine), and anus.
--Water vascular system: hydraulic system which
driven by water and muscular contraction serve to
motion of tube feet. These tube feet, small structures
with sucker-like endings, provide for locomotion and or
feeding.
-- Reproductive system -- Nervous system
-- Skeleton made of CaCO3 which is developed as
discrete plates or segments, each comprising a single
crystal of calcite. This monocrystalline structure is
particularly illustrated in the structure of spines of the
urchins.
Characters