12. Mollusca

Question 1

Mollusca

Answer 1

Lophotrochozoan
Triploblastic
Coelomate
Bilateral symmetry
Hydrostatic skeleton in some, Shell
No metamerism
Sexual - Monoecious or Dioecious
NO asexual
Organ-system
Open circulatory system - Closed in cephalopods

Question 2

Habitats of mollusca

Answer 2

Mostly marine

• Cephalopods all marine
• Bivalves and gastropods can live in brackish or freshwater

Question 3

Body structure of Mollusc

Answer 3

Head-foot
- Feeding, cephalic, sensory, locomotor organs
Visceral mass
- digestive, circulatory, respiratory, and reproductive organs

Question 4

Head-foot

Answer 4

Well developed head with mouth and sensory organs. (not bivalves)
Mouth contains structure unique to molluscs - radula

Question 5

Radula

Answer 5

Rasping protrusible, toungue-like organ found in most molluscs

Question 6

Foot

Answer 6

Adapted for locomotion and/or attachment
- Usually ventral
Modifications
- Bivalves: Laterally compressed
- Cephalopods: Siphon(a funnel) for jet propulsion

Question 7

Mentle

Answer 7

A sheath of skin extending dorsally from the visceral mass that wraps around each side of the body

• Protects soft parts
• Outer surface of the mantle secretes the shell

Question 8

Mantle cavity

Answer 8

Houses respiratory organs
- gills or a lung
Mantle’s surface participates in gas exchange
Products from digestive, excretory, and reproductive systems empty into the mantle cavity

Question 9

Reproduction of molluscs

Answer 9

Sexual reproduction only - Mostly dioecious

Most have free-swimming trochophore and veliger larval stages

Question 10

Trochophore

Answer 10

Minute
Translucent
Circlets of cilia

Question 11

Veliger

Answer 11

Free swimming
- Marine snails and bivalves
Develops from trochophore - Has the beginning of a foo, shell and mantle

Question 12

Circulatory system

Answer 12

Most molluscs have open circulatory system

• Hemolymph not confined to vessels
• Not as efficient as closed system - Common in slow-moving animals
• Cephalopods have a circulatory system

Question 13

Gastropoda

Answer 13

Molluscs
- Snails, limpets slugs etc
Many, but not all have shells
Terrestrial or aquatic
Bilaterally symmetrical
- Visceral mass is asymmetrical

Question 14

Adaptation in Gastropoda

Answer 14

All but few gastropods exhibit bilateral asymmetry

• Gill and kidney on the right side have been lost
• Water flows one way, left to right, clearing waste from the rectum

Question 15

Bivalvia

Answer 15

Two valves
Sedentary filter feeders
No head no radula
Very little cephalization

Question 16

Bivalvian sensory organs

Answer 16

Some bivalves have simple eyes - ocelli

Question 17

Ocelli

Answer 17

A simple eye or eyespot in many types of invertebrates

Question 18

Locomotion of bivalvians

Answer 18

Some are sedentary or sessile

Others can move slowly

Question 19

Cephalopoda

Answer 19

Most complex molluscs
Marine predators
Highly mobile
Vary in size
All are predators
Tentacles and arms used to capture prey
- Octopus and cuttle fish have salivary gland that secrete a venom for immobilizing
- Swim by jet propelling

Question 20

Shell of cephalopods

Answer 20

Ancestral cephalopods had shell

• Squid and cuttlefish have internal shell called a pen
• No shell in octopus

Question 21

Adaptations of cephalopods

Answer 21

Chromatophores
- Produce color changes in skin
- Associate with alarm or courtship
Ink sac