Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species

3. Mollusca are one of the most diverse groups of animals on
the planet, with at least 50,000 living species (and more
likely around 200,000) which range in size from 20-meter-
long giant squid to microscopic aplacophorans, a
millimeter or less in length, that live between sand grains.
It includes such familiar organisms as snails, octopuses,
squid, clams, scallops, oysters, and chitons.

4. • The word mollusc (or mollusk)
derives from the Latin word
“mollis,” which means “soft.”
 There are an estimated 200,000 species of mollusk worldwide accounting for nearly a quarter of all
marine life.
 They have a ribbon-like tongue, called the radula, covered in thousands of denticles (tiny teeth).
 Many have a calcium-carbonate shell.
 Most molluscs live in water, but slugs and snails live on land.

5. The African land snail can be
30 cm (12 in) long. It moves
slowly on a large, muscular
foot, using slime to ease the
way. Its mouth, underneath its
head, contains the denticle-
covered radula.

6. The blue-ringed octopus is a mollusc
that does not have a shell. It has a
large brain and big eyes. It uses its
eight arms to crawl, but also squirts
water from inside its body to move
more quickly.

7. According to fossil records, the first mollusks appeared
on earth some 600 million years ago.
It took another 100 million years before mollusks first
appeared in and near freshwater lakes and streams.

8. Molluscs have unsegmented bodies generally protected
by a shell. There are more than 50,000 species in seven
classes,
CLASSES OF MOLLUSCS:

9. 1. Class Aplacophora:
(“bearing no plates”) includes worm-like animals primarily found in
benthic marine habitats.
These animals lack a calcareous shell, but possess aragonite spicules
on their epidermis.

10. 2. Class Monoplacophora
(“bearing one plate”) posses a single, cap-like shell that
encloses the body.
The monoplacophorans were believed extinct and only
known via fossil records until the discovery of Neopilina
galathaea in 1952.
Neopilina connecting link between Annelida and
Mollusca
Neopilina is a highly derived genus of
modern monoplacophoran.

11. 3. Class Polyplacophora:
(“bearing many plates”) are commonly known as “chitons” and bear an armor-like, eight-plated dorsal
shell.
Chitons live worldwide, in cold water, warm water, and the tropics. Most chiton species inhabit intertidal
or subtidal zones.
And are exposed to the air and light for long periods.
Chiton morphology: The underside of the
gumboot chiton, (Cryptochiton stellari,)
showing the foot in the center, surrounded by
the gills and mantle. The mouth is visible to
the left in this image.

12. Several different kinds of algae growing on the
plates of this mossy chiton camouflage
Lined Chiton, Tonicella lineata

13. Class Bivalvia:
 Marine and freshwater molluscs with
laterally compressed bodies enclosed by a
shell in two hinged parts.
 Include clams, oysters, mussels, scallops,
and numerous other families of shells.
 Filter feeders and have no head or radula.
 The gills have evolved into ctenidia,
specialised organs for feeding and
breathing.
 Most bivalves bury themselves in
sediment on the seabed, while others lie on
the sea floor or attach themselves to rocks
or other hard surfaces.
 also known as pelecypods.
The world's largest clam (187 cms), a Sphenoceramus
steenstrupi fossil from Greenland in the Geological
Museum in Copenhagen

14. Empty shell of a bivalve: The empty shell of
the giant clam, Tridacna gigas. Note the pair
of shells that are hinged together, a
characteristic of members of the class
Bivalvia.
Different bivalves shells

15. Class Gastropoda:
(“stomach foot”) include well-known mollusks like snails,
slugs, conchs, sea hares, and sea butterflies.
These animals are asymmetrical and usually present a coiled
shell.
Shells may be planospiral (like a garden hose wound up),
commonly seen in garden snails, or conispiral (like a spiral
staircase), commonly seen in marine conches.
key characteristic of this group, along with a foot that is
modified for crawling.
Most gastropods bear a head with tentacles, eyes, and a style.
Gastropod foot: Gastropods, such as this
Roman snail, have a large foot that is
modified for crawling.

16. Sea hare (Aplysia californica) emitting
ink cloud
This gastropod molluscs with a soft internal shell
made of protein. And also used in the study of
memory loss.
Cone Snail is also known as the “cigarette snail”.
Amazing fact is one drop of venom from it is enough to
end 20 human lives. You die within minutes and there
is no antivenom.

17. 6. Class Cephalopoda
 (“head foot” animals) includes octopus, squids, cuttlefish, and
nautilus.
 They display vivid coloration, typically seen in squids and
octopus, which is used for camouflage.
 Carnivorous predators and have beak-like jaws at the anterior
end.
 Locomotion in cephalopods is facilitated by ejecting a stream
of water for propulsion (“jet” propulsion).
 Cephalopods, such as squids and octopi, also produce sepia or
a dark ink, which is squirted upon a predator to assist in a
quick getaway.
 Suckers are present on the tentacles in octopi and squid.
(“head foot”) include this octopus,
which ejects a stream of water from a
funnel in its body to propel itself
through the water.

18. Self-defense in cuttlefish
 Cuttlefish are eaten by various species of predator fish,
dolphins and people.
 They have three ways to defend themselves.
 First of all, they can swim backwards at an incredible
rate using their ‘jet motor’.
 Secondly, cuttlefish can emit a cloud of ink. The ink
blocks the attacker’s vision and knocks out its sense of
smell.
 Thirdly, the animals use camouflage: they can change
color very quickly and take on the color of their
surroundings.
Squid are often called ‘the chameleons of
the sea’. Perhaps it is better to call the
chameleon ‘the squid of the land’.

19. 7. Class Scaphopoda
(“boat feet”) are known colloquially as “tusk shells” or “tooth shells,”
Usually buried in sand with the anterior opening exposed to water.
These animals bear a single conical shell, which has both ends open.
These animals do not possess eyes, but they have a radula, as well
as a foot modified into tentacles with a bulbous end, known as
captaculae.
Captaculae serve to catch and manipulate prey.
Ctenidia are absent in these animals.
Antalis vulgaris, the shell of which is
depicted here.
Shells of the species Dentalium
pretiosum were used as money.

20.  Freshwater molluscs are common in ponds, lakes, quiet water pools, and flowing waters like
perennial rivers, irrigation canals, etc.
 Gastropods are generally found attached to submerged vegetation, rocks, sticks, bricks, etc., but
bivalves live partly buried in the sand or mud.
 Primarily inhabitant of the intertidal and littoral zones of the oceans molluscs descend into a
greater depth.
 Most mollusks are marine animals that live in habitats from shallow coastal areas to deep waters.
Most stay within the sediments at the bottom of water bodies, although a few—such as cephalopods—
are free swimming.
Habitat:

21.  With the exception of cephalopods, mollusks are by and large gentle vegetarians.
 Terrestrial gastropods like snails and slugs eat plants, fungi, and algae, while the vast
majority of marine mollusks (including bivalves and other ocean-dwelling species)
subsist on plant matter dissolved in the water, which they ingest by filter feeding.
 The most advanced cephalopod mollusks—octopuses, squids, and cuttlefish—feast on
everything from fish to crabs to their fellow invertebrates; octopuses, in particular,
have gruesome table manners, injecting their soft-bodied prey with venom or drilling
holes in the shells of bivalves and sucking out their tasty contents.
DIET OF MOLLUSCS

23. Cuttlefish eating fish

24.  Mollusks generally reproduce sexually, although some (slugs and snails) are hermaphrodites, they still
must mate to fertilize their eggs.
 Eggs are laid singly or in groups within jelly masses or leathery capsules.
 The eggs hatch into veliger larva—small, free-swimming larvae—and metamorphose into different stages,
depending on the species.
Reproduction and Offspring

25. Squid (Loligo opalescens) pair mating, with egg
cases on ocean floor
In oyster, occurs external fertilization
Male and female release the sperms and
eggs in water

26. Whelk egg cases

27. Amazing Cluster of Octopus Eggs Squid Eggs
Giant river snail laying hot pink eggs

28. • Estimation of global diversity of molluscs varies from 80,000 to 1,00,000.
• According to one estimate there are
62,000 species of gastropods
9200 species of bivalves
500 species of polyplaphora
400 species of cephalopods
300 species of scaphopods
130 species of aplacophorans
5 species of monoplacophorans.
• A more conservative estimate gives the number as 31,663 marine, 8765 freshwater
and 24,503 terrestrial species, total 64,931.
Diversity of Mollusca of world:

29. In India, till today, 5155 species of Mollusca have been recorded,
• from freshwater (22 families, 53 genera 183 species), land (26
families, 140 genera and 1487 species)
• from marine habitats (242 families 591 genera, 3400+ species)
Diversity of Mollusca of India:
(Subba Rao, 1991, 1998, 2000; ZSI, 2011).

33. IMPORTANC OF MOLLUSCS

34. • Molluscs play important roles in almost every known ecosystem on land and in the sea.
• Many molluscs are links in food chains, the pathways and the animals that are food for humans
and other animals.
• Nearly 20% of reef fishes feed on molluscs in the coral reef ecosystem.
• Throughout the world oceans, squids and octopus are the animals on which fishes, whales,
dolphins, and sea birds mainly feed.
• Sustainable use of molluscs in the long run may pave way for the restoration of species balance
in nature, especially in the ecologically sensitive, biotically rich, fragile areas like sea grass,
mangrove and coral reef ecosystem

35. Molluscs have lost much of their historical usage as medicine,
tools or religious symbols but their economic value as a source of
protein and as ornaments or decorations is possibly greater now
than ever before.

36. Ornamental shells are still traded in huge quantities and perhaps
even more so today because of the increase of trade via electronic
media especially Internet.
Throughout the world, gastropod, cephalopods and bivalve shells
are bought or collected as 'portable memories' when people are
vacationing.
Tropical shells, with their attractive colours and hues, various
morphologies with intricate spikes and curves, are especially
popular souvenirs.

37. The development of international and local tourism in the
tropics over the last three decades has increased the
demand and trade in souvenirs, with consequent
pressures on marine resources.

38. Economic Importance
 The livelihood of these regions rely on the abundance and availability of
molluscs to survive.
 The reliance on this protein source parallels the predation phenomenon
discussed in the previous section.
 As human populations continue to exponentially increase protein sources
derived from fish, crustaceans and molluscs account for 16.5% of animal protein
intake globally.
Nutritional Resource

39.  If Molluscan populations decrease, reduction of population of all marine phyla
utilized as a protein source for humans will occur.
 Currently, two-thirds of global marine food supply is obtained from off-shore
and inland waters.
 The increase in dietary recommendation for consuming fish has lead to
concerns about the sustainability of maintaining harvest for demands without
depleting this resource.
 In the United States alone, approximately 300,000 pounds of various Mollusca
species were harvested in 2013.

42. What are the Threats ?
• Destruction of their habitat and depredation by humans, but that's not the case for
freshwater mollusks (i.e., those that live in lakes and rivers) and terrestrial (land-
dwelling) species.
• Lakes and rivers are also prone to the introduction of invasive species, particularly
mollusks which travel attached to international seagoing ships.
• Sand mining
• Tourism
• Trade of sea shell

43. Why we need to protect Mollusca ?:
• Several edible and commercial species fall in to the conservation category,
and demonstrates how heavy demand and intensive fishing can have a
considerable impact on population as a whole, even though the species
themselves are at the risk of extinction.

44. Pugilina (Hemifusus) cochlidium, a Crown Conch is often used
as medicinal purpose by the tribal people of West Bengal
especially people from Sunderbans.
In West Bengal Crassostrea gryphoides (Kausturi Jhinuk) and
Anadara granosa (Padma Jhinuk), a huge number of dead and
living shells are used as calcium resources in the poultry feed.
Crown Conch
Anadara granosa

45. • Found in Andaman and Nicobar as well as Lakshadweep groups of Islands.
• Population of the larger species of Giant Clams (Tridacnidae) has declined
dramatically in many parts of the Indo Pacific as a result of over collecting
both for shell and meat.
• The Giant Triton Charonia tritonis, which occurs naturally at low densities
seems to have become rare in recent years.
• For this reason, this species is included in the Schedule I of the Wildlife
(Protection) Act, 1972 of India.
Gaint Clams (Tridacna spp. )
Charonia tritonis
( Triton's trumpet or
giant triton)
which occurs naturally
at low densities, has
become rare through
over-collection.

46. Chank (Turbinella pyrum) is restricted in its distribution, which
occur at a depth from 30 m to 45 m in the Gulf of Manner and at
lesser depth in the Gulf of Kachchh are fished at regular intervals.
Species viz.
Chank (Turbinella pyrum)
Trochus niloticus and Turbo marmoratus are two commercially
important gastropods. Both the species are distributed in the
coral reefs of Andaman and Nicobar Islands and occur up to 20 m
depth.
Trochus niloticus Turbo marmoratus
Use of Chank

47. The shells, of the Placuna Bruguiere, and of cockles (Chiefly
Cardiidae), are used in the manufacture of tooth pastes. The shells
are collected in Tuticorin and sent to Calcutta and Madras for this
purpose (CSIR, 1962a).

48. Conservation Status of
Molluscs:
 Insufficient information on status of the population (wild stocks) and optimum level of exploitation of
marine molluscs in India is known.
 Determination of the status of many Mollusca is the need of the hour to provide protection and
conservation.
 Data on the life history, abundance, productivity and rates of exploitation from specific localities are
essential for every species involved in the shell trade.
 Recently it is noticed that conservation problems are on the increase and makes it possible to predict
which areas and species are most vulnerable

49.  Similarly, the Operculum of Pugilina (Hemifusus)
cochlidium, a crown conch, is used for its medicinal
value “Sanka Bhasma” by the coastal dwellers of West
Bengal, especially fisher folk in Sunderbans.
 The bivalve Meretrix meretrix is extensively used in
the manufacture of poultry feed and lime and is
collected by the tone from the Subarnarekha River in
Odisha and West Bengal

50. Nalu kasu coin depicting sacred chank
(Trivandrum)

51. Conservation Measures:
There are several action that may be taken,
 Control trade in shells, and thus avoid over - exploitation and habitat damage.
 Manage the fishery properly, used in sustainable manner.
 Government of India should implement species specific management programmes and
regulate exports, and importing countries can control imports.
 The problems would also be lessened if demand for ornamental shells declined.
 A greater “public” awareness of the conservation issues could help in this respect.

52.  Conservation and management of population of molluscs in the long run may pave way for
restoration of species balance in nature, especially in the ecologically sensitive, biotically rich,
fragile ecosystems such as coral reef, mangrove and sea grass.
 There are several rules and regulations formulated by the Government of India to protect
conservation of marine biodiversity.

53. CONSERVATION MEASURES BY GOVERNMENT OF INDIA:

54.  The Ministry of Environment, Forest and climate change promulgated 24 species of marine mollusc
under Schedule I (9 species) and IV (15 species) of the Wildlife (Protection) Act, 1972.
 The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) provides
a means of controlling international trade in species considered to be seriously threatened.
 At present, the only marine molluscs listed are the giant clams (Family Tridacnidae).
 These are listed in Appendix II, which means that a valid export licence is required from the country of
origin before the shells, meat or live animals can be traded between the parties to the convention.

55. Legislation for protection of mollusca
Sea ranching of Mollusca also done by govt.
ranching for enhancing molluscan diversity,
sustainable utilization and conservation.

56. Collector of the shells should understand the importance of
conserving stocks, and using selecting methods which do not
damage the habitat.
Guidelines or instructions could be produced for both
commercial collectors and tourist. The suggested codes of
conduct are:
1. Eggs, juveniles and breeding groups should not be taken.
2. Shells with defects should not be taken (these are in any case
generally unsalable “specimen” shells)..
3. The habitat should be disturbed as little as possible.
4. Living attached corals should not be touched.
5. If stones, loose coral or boulders are moved, they should be
returned to their original positions.
Improved collecting methods:

59. It is suggested that general awareness can be made through,
• Various seminars, symposium
• Short documentary attractive films
• Training programmes to make aware to the common people
• Coastal inhabitants
• College students
• School children's even to the forest rangers about the conservation
of molluscs, role of molluscs in the ecosystems.
Power of knowledge exercised by the common people is evidently a
great tool for conservation of nature and natural resources
Awareness:

61. • Dey, A. (2006). Contribution to the knowledge of Indian Marine molluscs (Part – IV) Family Tellindiae.
Rec. Zool. Surv. India., Occ. Paper No. 249: 1-124, 38 pls.
• Dey, A. (2008). Commercial and medicinal important molluscs of Sunderbans. Rec. Zool. Surv. India Occ.
Paper No. 286: 1-54.
• Ramakrishna and Dey, A. (2010). Manual on identification of Schedule mollusks from India, Zoological
Survey of India, 40 p.
•Subba Rao, N.V. (2003). Indian Seashells (Part I), Polyplacophora and Gastropoda. Rec. Zool. Surv. India,
Occ. Paper 192: 1-416.
• Subba Rao, N.V., and Dey, A. (1984). Contribution to the knowledge of Indian marine molluscs. 1. Family
Mitridae. Zool. Surv. India, Occ. Paper 61: 1-48.
•Subba Rao, N.V., and Dey, A. (1986). Contribution to the knowledge of Indian marine molluscs. 2. Family
Donacidae. Zool. Surv. India, Occ. Paper 91: 1-30.
•Tikader, B.K. and Das, A. K. (1985). Glimpses of animal life of Andaman and Nicobar Islands. Zoological
Survey of India, Kolkata. 170 p.

62. • Tikader, B.K., Daniel, A. and Subba Rao, N.V. (1986). Sea shore animals of Andaman and Nicobar Islands.
Zoological Survey of India, Kolkata. 188 p.
•Sturm, Charles F., Timothy A. Pearce, Ángel Valdés (eds.). "The Mollusks: A Guide to Their Study,
Collection, and Preservation." Boca Raton: Universal Publishers for the American Malacological Society,
2006.
•Fyodorov, Averkii, and Havrila Yakovlev. "Mollusks: Morphology, Behavior, and Ecology." New York:
Nova Science Publishers, 2012.