Phylum Mollusca

1
Phylum Mollusca

• Characteristics
• 90,000 living species 70,000 fossil
• Soft body
• 80 under 10 cm
• Most marine some freshwater or terrestrial
• Coelom is a chamber around heart

2
More Characteristics

• Feeding
• Herbivorous grazers
• Predaceous carnivores
• Filter feeders
• Parasites

3
Examples

• Chitons, tusk shells, snails, slugs, nudibranchs,
  sea butterflies, clams, mussels, oysters, squids,
  octopuses, nautiluses

4
Economics

• Food
• Pearl culturing
• Destructive burrowing shipworms
• Garden pests (snails, slugs)
• Intermediate host for parasites (snails)

5
Form and Function

• Body Plan
• Head-foot
• Feeding, sensory, locomotor organs
• Visceral mass
• Digestive, circulatory, respiratory, reproductive
  organs

6
Head-Foot Structure

• Mantle and cavity
• Head with mouth, sensory organs
• Simple to complex eyes
• Tentacles in some
• Radula
• Visceral mass
• Foot (locomotion)

7
Radula details

• In all except bivalves
• Tongue-like
• Rows of tiny teeth
• Conveyor belt to digestive tract

8
Foot details

• Usually ventral
• Locomotion or attachment
• Some modifications
• Burrowers anchor
• Free-swimmers fin
• Squidssiphon jet

9
Visceral Mass

• Mantle
• 2 folds of skin
• Surface functions in gas exchange
• Mantle cavity
• Shell

10
Mantle Cavity

• Space between mantle and body wall
• Contains gills or a lung
• Gills leaf-like, cilia propel water
• Collects digestive, excretory, reproductive
  products
• Jet propulsion

11
Shell layers

• Secreted by mantle
• Periostracum (outer)
• Prismatic (calcium carbonate)
• Nacreous (thin layers next to mantle)

12
Internal Structure

• Circulatory system
• Open heart, vessels, sinuses
• Closed heart, vessels, capillaries
  (cephalopods)
• Kidneys or metanephridia
• Nervous system (ganglia)

13
Reproduction

• Most dioecious some monoecious
• Trochophore larva (free-swimming)
• Direct metamorphosis (chitons)
• Veliger--Indirect metamorphosis (most gastropods
  bivalves)

14
Classes

• Caudofoveata
• Solenogasters
• Monoplacophora
• Polyplacophora (chitons)
• Scaphopoda
• Gastropoda
• Bivalvia (Pelecypoda)
• Cephalopoda

15
Class Caudofoveata

• Small, wormlike, marine, burrowers
• Radula present
• Scales, no shell
• Few species
• Resemble ancestral form of molluscs

16
Solenogasters

• Resemble caudofoveates, but no radula or gills
• Do not burrow
• Feed on cnidarians
• Few species

17
Monoplacophora

• Very few species
• Small rounded shell
• Radula present

18
Polyplacophora (Chitons)

• 8 dorsal plates
• About 1000 species
• Photosensitive structures
• Radula present
• 3-chambered heart metanephridia
• Dioecious
• Direct metamorphosis of trochophore larva

19
Scaphopoda

• About 900 living species
• Mantle wrapped around viscera fused to form tube
• Burrowing foot
• No gills gas exchange via mantle
• Cilia on foot trap prey
• Radula and gizzard present