Phylum mollusca

Phylum mollusca

1. Phylum Mollusca “Soft Bodied Animals”

2. Phylum Mollusca Second largest phylum Soft bodied animals, most with calcified shell Four main classes: Gastropoda, Bivalvia, Polyplacophora, Cephalopoda

3. Characteristics of Phylum Mollusca Body Type: Bilateral Symmetry Body Organization: Triploblastic 3 Layers – Endoderm, Mesoderm, Ectoderm Body Cavity: Coelom

4. Body Plan All molluscs have four basic parts to their body: Foot – Takes many forms, used for locomotion Mantle – Outer covering of the body Visceral Mass – Internal organs Shell – Lost or reduced in some classes

5. Digestive System: Complete – mouth and anus separate Specialized feeding structures: Gills, Beak, Radula

6. Circulatory System: Open (Gastropoda, Bivalvia, Polyplacophora) Heart pumps blood from gills to open space around organs Slow moving lifestyle has lower oxygen demands Closed (Cephapopoda) Heart pumps blood within blood vessels Active lifestyle, large size has higher oxygen demand and requires more efficient circulation

7. Reproduction Sexual : Most are dioecious, some hermaphrodites (gastropods) Internal or external fertilization Fertilized egg develops into trochophore larva: Free swimming, planktonic larva that feeds on tiny plants. Also found in Annelida suggesting a common evolutionary ancestor Asexual : Some regeneration

8. Nervous System Nerves and ganglion Brain present in cephalopods Sensitive touch and chemoreceptors Eyespots for light detection Image producing eyes found in cephalopods

9. Respiration Gills exchange of gases in aquatic environments Terrestrial molluscs have modified gills inside their mantle cavity – require moist environment. Excretion Nephridia & anus

10. Ecological Roles Molluscs fill a wide variety of ecological niches Predators, filter feeders, food source Break down decaying plant matter Filter feeding bivalves can be an indicator of water quality Shipworms (not worms) burrow through wood boats and docks Terrestrial molluscs are agricultural pests