Phylum Mollusca

Question 1

Economic Importance Of Mollusca

In terms of growth inhibition
In terms of disease vectors
In terms of ornaments
In terms of farm plants destruction
In terms of religion

Answer 1

The extracts of hard-shelled clams are the growth inhibitors of cancers in mice
They serve as vectors of some diseases e.g Schistosomiasis
The shells are used for making ornaments and jewelleries
Destruction of farm plants E.g Garden Snail(Achatina spp.)
The sacred chanks have played a major role in Indian religion. It is held in high esteem by Hindus

Question 2

Economic Importance Of Mollusca

In terms of food
In terms of material exchange
In terms of food chain
In terms of fishing industry
In terms of fish poisoning

Answer 2

Many gastropods, bivalves, cephalopods are source of food for many cultures
Use of cowries as money
They are of great importance within food chains and in the ecosystem
They play an important role in the fishing industries of many countries
Some clams and mussels are carriers of paralytic shell fish poisoning

Question 3

Classification Of Mollusca

Answer 3

1. Polyplacophora E.g Chitons
2. Gastropoda E.g Snails, Slugs
3. Bilvalvia E.g Clams, Oysters, Scallops & Other Bilvalves
4. Cephalopoda E.g Squids, Octopuses and Nautiluses
5. Monoplacophora E.g Neopolina
6. Scaphoda E.g Tusk, Tooth Shells

Question 4

Characteristics Of Mollusca

In terms of shell
In terms of body plan
In terms of mantle
In terms of length
In terms of squids and octopuses

Answer 4

Most molluscs are protected by a hard shell made of calcium carbonate
They all have similar body plan; which has 3 main parts
The mantle extends beyond the visceral mass producing a water filled chamber, mantle cavity which houses the gills, anus and excretory pores
They vary in length from clams(<1mm) to giant squids(that exceed 18m)
Squids and Octopuses have reduced shells that have been internalized, or they have lost their shells completely during their evolution.

Question 5

Characteristics Of Mollusca

In terms of phylum description
In terms of group diversity
In terms of body type
In terms of species
In terms of habitat

Answer 5

A large phylum of invertebrate animals E.g Snails, with a soft body lacking segments and usually enclosed in a shell containing calcium
It is one of the most diverse groups of animals on the planet
They are soft bodied animals
There are about 100,000 known species
Mostly inhabit marine, freshwater and snails & slugs that live on land

Question 6

Characteristics Of Mollusca

In terms of fertilization
In terms of sexes
In terms of feeding
In terms of development
In terms of circulatory system

Answer 6

Fertilization may be internal or external
The sexes are usually separate; although many snails are hermaphroditic
Many molluscs feed by using a strap like rasping organ called Radula
Some snails as well as octopuses and squids have direct development, embryo develop into miniature replicas of the adults
Most molluscs have an open circulatory system in which haemolymph; a blood-like fluid, leaves the circulation vessels and bathe tissue directly.

Question 7

Radula

Answer 7

A belt of backward curved teeth that extends from the mouth and slides back and forth

Question 8

Body plan of a mollusc

Answer 8

Muscular foot- Used for movement
A visceral mass- Contains most of the internal organs
A mantle- A heavy fold of tissue that drapes over the visceral mass and may secrete a shell