1. PHYLUM MOLLUSCA (Molle= soft body)

2. PHYLUM MOLLUSCA
OVER 100,OOO LIVING SPECIES; MANY 1000’S OF FOSSIL SPECIES
FOUND IN ALMOST ALL ENVIRONMENTS: MARINE, FRESHWATER, TERRESTRIAL
INCLUDES SNAILS, SLUGS, CLAMS, SQUIDS, OCTOPUSES,

3. CHARACTERISTICS Body Plan: three main parts- head, foot, visceral mass
body is unsegmented

4. CHARACTERISTICS
Mantle - specialized tissue, secretes shell, may be involved in feeding, reproduction and respiration
Radula – for rasping; in all but one class
Radula closeup

5. ALL ORGAN SYSTEMS ARE PRESENT
Circulation - Open (Hemocoel) - Hemocyanin
Respiratory System - gills (Ctenidia), lungs, mantle, epidermis
Osmoregulation - Metanephridia also excretion

6. ALL ORGAN SYSTEMS ARE PRESENT
Feeding - Radula (scraping)
Bivalves - Filter feed
Nervous System - Complex system of Ganglia

7. ALL ORGAN SYSTEMS ARE PRESENT
Reproductive System - usually dioecious, monoecious in some
Marine forms have free living trochophore larva
Other larval stages may be present

8. MOLLUSCAN CLASSES

9. Class Monoplacophora “one plate”
all known from deep marine waters (>12,000 feet)
have a single circular shell
with radula

10. Class Polyplacophora “many plates”- (chitons)
have 8 overlapping plates or shells
reduced head, no eyes or tentacles
all marine; usually live on rocky shores
have radula, gills
external fertilization
scrape algae

11. Polyplacophora Respiration - Gills in pallial groove
Circulation - Heart at posterior end - single Aorta
Excretion - Nephridia
Nervous System and sense organs - Ganglia and nerves
Sub Radular organ - Feeding
Esthetes - light sensing
Osphradia - Sampling water

12. Polyplacophora Reproduction - Sexes Separate
Usually external fertilization
Trochophore larva

13. Class Aplacophora “without plates”
Rare; lack shell; wormlike
deep marine; burrowing species; predators
About 320 species, not much is known of them
Your book separates them into two separate classes:
! Caudofoveata
! Solenogastres

14. Class Gastropoda Largest class of Molluscs
Most important feature is Torsion

15. Torsion Twisting of body into loop Perhaps adaptation of veliger larva
Disadvantages:
Reduction of organs on right side
Excretion - Mouth moves near anus
Adavntages
Allows water to be drawn from the front

16. Gastropod - Locomotion
Foot
Ciliary action below the foot
Operculum
Swimming

17. Gastropod - Nutrition Herbivores - Radula Carnivores Filter feeders
NERVOUS SYSTEM
Similar to Chiton - but in the shape of “8”

18. Class - Bivalvia Includes Calms, Oysters, Mussels
Has two Shells (Valves)
Shell held together by Adductor muscle
Head is lost
Filter feeders
Mantle secretes the shell

19. MOLLUSCAN SHELL STRUCTURE
Periostracum; outer layer
Prismatic; middle layer
Nacre; inside layer- mother of pearl

20. BIVALVIA Locomotion Circulation Excretion Foot (burrowers)
Active swimmers (Scallops)
Circulation
Open system
Excretion
Nephridia

21. BIVALVIA Nervous System Reproduction 2 pairs of ganglia
Sense organs (statocysts, ocelli, ospharidia)
Reproduction
Sexes separate
Internal fertilization
Larva - Glochidium

22. Class - Cephalopoda Includes Squid, octopus, Nautilus
Most advanced of Molluscs
Well developed head and eyes
Head has tentacles with suckers
Squids are largest of invertebrates
Locomotion by jet propulsion

23. Class Scaphopoda (tusk shells)
slender, tubular shells open at both ends
all marine
have tentacles around mouth
no defined head
no gills, respiration across mantle