Phylum Mollusca

1) True coelomic animals

2) Belong protostomates have blastopore

3) All organ systems present and well-developed

4) Tcochophore larva: Free-swimming ciliated marine larva

 

Biological Contributions

1) Radula---> rasping organ

2) Respiratory organs (lungs, gills) gas exchange.

3) Mantle: secretes shell or can be modified for different uses.

4) Open circulatory system: heart, vessels, blood sinuses.

5) Some of largest invertebrates due to respiratory system and coelomic cavity.

6) Foot: muscular organ used primarily in locomotion.

7) "Skin" eye: highly developed comergent with "brain" eye.

8) Terrestrial and aquatic - marine\freshwater

9) Secondary cavity within mesoderm

10) Mesodermal epithelium parietal to peritoneum.

11) Mesentary continuous of peritoneum.

12) Organs covered in visceral peritoneum

13) No crowding. Stable arrangement

14) Coelomic fluid usually ciliated lining through aids in movement in wastes and food.

15) Parity also acts as hydrostatic skeleton; variety of movements can be produced via contraction of muscles.

16) All higher vertebrates and invertebrates have coelom.

17) Molluscs don't seem to really take advantage of it; theirs is limited to a space around heart. Sometimes gonads and part of kidney.

 

Characteristics of Molluscs

1) Bilateral symmetry (some bilateral asymmetry) and usually with a definite head.

2) Ventral body wall is specialized as muscular foot; mainly for locomotion

3) Dorsal body wall forms a pair of folds (mantle); secretes shell (absent in some) modified into gills or lungs. Mantle is ectodermal\coelomic cavity mesodermal.

4) Surface epithelium usually ciliated with mucous glands and sensory nerve endings. Secreted mucous aids locomotion; forms "slime trait" in some.

5) Coelom limited to area around heart, perhaps lumen of gonads or kidneys.

6) Anus usually empties into mantle cavity. Complex digestive system : radula.

7) Open circulatory system (mostly closed in cephalopods) usually three chambered heart, blood vessels, sinuses, blood pigments.

8) Gaseous exchange in lungs, gills, mantle, or body surface.

9) One or two metanephridia (kidneys) emptying into mantle cavity. Tubular, tissue structure physically removing wastes.

10) Nervous system of pairs; cerebral, pleural, pedal, and visceral ganglia. Nerve cords, subepidermal plexus, ganglia are centralized in nerve ring in gastropods and cephalopods.

11) Sensory organs of touch, taste, smell, equilibrium and vision ("skin" eye); eyes highly developed in cephalopods.