General Zoology Mollusca

Molluscs range in size and body form from the giant squid, measuring 18 meters in length, to the smallest garden slug, less than one centimeter long. In spite of this diversity, the phylum Mollusca is not difficult to characterize. See table.

Phylum Mollusca

1. Body of two parts: head-foot and visceral mass

2. Mantle that secretes a calcareous shell and covers the visceral mass

3. Mantle cavity functions in excretion, gas exchange, elimination of digestive wastes, and release of reproductive products

4. Bilateral symmetry

5. Protostome characteristics, including trocophore larvae, spiral cleavage, and schizocoelous coelom formation

6. Coelom reduced to cavities surrounding the heart, nephridia, and gonads

7. Open circulatory system in all but one class (Cephalopoda)

8. Radula usually present and used in scraping food

Miller, S.A. and J. Harley. Zoology. 5^th Edition. McGraw-Hill: New York, 2002.

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