1. Biology 11 Kingdom Animalia
Phylum Mollusca:
The Soft Bodies

2. Phylum Mollusca Objectives
State why Molluscs are more advanced than Nematods
Describe the 3 defining characteristics of Molluscs
Describe the 7 Classes and example animals
Know squid anatomy

3. Phylum Mollusca Mollusca = soft bodies
Second largest phylum of animals
Characteristics:
Three defining traits:
1. Large ventral muscular foot
2. Visceral mass located dorsal to the foot
3. Tissue layer called “mantle” covers the visceral mass

4. Phylum Mollusca Evolution
Likely a similar ancestor as annelids, due to:
1. Same type of larvae (Trochophore Larvae)
2. Evidence of segmentation seen in larvae and primitive members of this phylum

5. Class Monoplacophora (AKA: one plate)
The first mollusk, now considered a living fossil: thought to be extinct until one was found in Costa Rica in the mid 1950s
Looks like a limpet but found in the deep ocean.

6. Class Polyplacophora (AKA: many plated)
The Chitons
Exclusively marine
Have 8 dorsal plates
Primitive with segmentation have radula scrapers to feed on algae

7. Class Aplacophora (AKA: naked molluscs)
Lack a shell, secrete calcium-based spicules instead and appear shiny
worm-like animals found deep in the ocean

8. Class Gastropoda (AKA: stomach foot)
Largest class.
May or may not have a shell (slugs)
Live in fresh, salt water, and land
Contains single spiral shell
Well developed senses
Snails, slugs & nudibranchs
Nudibranch
Banana Slug

9. Gastropoda torsion: rotation of digestive system

10. The Radula

11. Class Scaphopoda (AKA: shovel foot)
Live burrowed in the marine mud, head down
Tusk shaped shell is open at both ends (unique!!)
Ex animal: tusk shelled organisms

12. Class Bivalvia (AKA: 2 shells)
Contain 2 hinged shells (valves)
Filter feeders, sessile
Use gills for respiration & filter feeding
Includes: clams, oysters, scallops, mussels
Clams
Mussels

13. Class Cephalopoda (AKA: head foot)
Octopus
These are the most highly evolved invertebrates
Have vertebrate eye (parallel evolution)
Capable of learning
Very motile predators - largest invertebrate
Shell greatly reduced
Squid

14. The cuttlefish and nautilus
Class Cephalopoda
The cuttlefish and nautilus
Cuttlefish

15. Clam re-section diagram: