The shells of molluscs have 3 layers. Which is not one (nacreous/mantle/periostracum)?

All mollusks have a muscular foot, mantle and visceral mass. Look for these structures and compare them between the representative marine bivalve and terrestrial gastropod. Relate how these differences fit their lifestyle.

For phylum Mollusca, Class Cephalopod  1. Characteristics. List whether the organism is:a. Diploblastic or triploblastic (if applicable) b. Deuterostome or protostome (if applicable) c. Coelomate, pseudocoelomate or eucoelomate (if applicable)    2. Organ/system characteristics. Answer the following for each organism:a. How is their circulatory system? b. Excretory/osmoregulation: How does the organism eliminate waste? What organs do they use?   3. Ecology. Describe/answer the following for each organism:a. Does it have a complete or incomplete digestive system? How does this animal feed?b. Identify any unique feeding structure• Be sure to use the correct terms to identify any unique feeding structure(s) used by the animal.

The opening of a gastropod shell is called the (spire/aperture/whorl/spine)