1. ZOO 115 Invertebrate Zoology
Mollusca

2. Mollusca – Classes Monoplacophora Aplacophora Polyplacophora
Gastropoda
Bivalvia
Scaphopoda
Cephalopoda

3. Mollusca – Class Monoplacophora
Gills
Mantle Cavity
Mantle
Resemble the generalized mollusc
Small (3 mm), flattened molluscs that inhabit deep water
Present in the Cambrian period – thought to be extinct until 1952
Single shell
animaldiversity.ummz.umich.edu/site/resources/Grzimek_inverts/Monoplacophora/Laevipilina_antarctica.jpg/medium.jpg
Foot
Anus
Mouth

4. Mollusca – Class Aplacophora
Mouth
~ 300 species
Small benthic dwellers between m
Shell-less
Secrete calcareous spicules on epidermis
Foot reduced or absent
No eyes, tentacles, statocysts, or nephridia
Pedal groove or foot
Gills
Mantle Cavity

5. Mollusca – Class Polyplacophora
Ancient (since late Cambrian)
Lives in rocky-intertidal region
Has series of plates for a shell.
It is an herbivore (except for one species)

6. Mollusca – Class Polyplacophora

7. Mollusca – Class Gastropoda
Marine and terrestrial
2nd largest class in animal kingdom
Hard shell (most)

8. Mollusca – Class Gastropoda variety

9. Mollusca - Class Gastropoda
Herbivores and predators.
Has a radula
Hard shell (most)
Well developed head and cephalic tentacles
Locomotion – peristalsis of foot.

10. Mollusca – Class Gastropoda Anatomy/

11. Mollusca – Class Gastropoda - foot
Columellar muscle
Retracts head and foot into shell
Extends head and foot
Twists foot
Tarsos muscle
Bottom of foot and edges
Locomotion
Prey capture
Molding of eggs
No fluid filled hemocoel /
How can it do both?
Columellar muscle
Tarsos muscle

12. Mollusca – Class Gastropoda Shell Coiling
Uncoiled
Planospiral
Whorl

13. WHY? Torsion 180◦ counterclockwise rotation of visceral mass
Torsion
180◦ counterclockwise rotation of visceral mass
Anus position
Gill position
WHY?

14. Torsion - WHY?
Larval theory – allows foot to be brought up into shell

15. Torsion - WHY? Adult theory –
allows for better ventilation of mantle cavity and gills
Places osphridium anteriorly
May help increase efficiency of creeping with a coiled shell

16. Problem from torsion Sanitation Slits or holes to accommodate waste
Unidirectional flow of water

17. Class Gastropoda - Diversity
Subclass – Prosobranchia
Order Archeogastropoda
Order Mesogastropoda
Order Neogastropoda
Subclass Ophistobranchia
Subclass Pulmonata
Molecular evidence indicates that these classifications are no longer valid!

18. Subclass Prosobranchia -
Usually with a spirally coiled shell (whorl)
Mantle cavity anterior
Osphridium (not shown)
Gills
Anus
Nephridiopore (not shown)

19. Order Archeogastropoda
Primative
Herbivores
Radula has numerous teeth in transverse rows
1-2 bipectinate gills
Mantle cavity without siphon
Sexes separate

20. Order Archeogastropoda
Abalone
Keyhole limpets
Limpets*
* Order Patellogastropoda

21. Order Mesogastropoda Cerithidae Cassidae Olividae Vermetidae
Cerithidae
Cassidae
Olividae
Vermetidae
Turritellidae
Cypraeidae
Tonnidae
Hydrobia
Capulidae
Janthinidae
Calyptraeidae
Strombidae
Naticidae
Carinaridae

22. Order Mesogastropoda Operculum present Radula with seven teeth/row
Operculum present
Radula with seven teeth/row
Only left gill – unipectinate
One atrium
One nephridium

23. Order Neogastropoda

24. Order Neogastropoda Entirely marine
Radula with 3 or fewer teeth per row
One gill
One atrium
One nephridim

25. Order Neogastropoda

26. Mollusca – Order Neogastropoda Cone snail