7. Label this diagram of an annelid and identily its class (Oligochacta, Polycha

Question

7. Label this diagram of an annelid and identily its class (Oligochacta, Polychaeta, or Hirudinea). 19.2 Mollusks (Phylum Mollusca) s. Explain what causes the growth ridges found on the shells of bivalves 9· List some structures that distinguish bivalves from the other molluscan classes. 10. What characteristics distinguish slugs from nudibranchs? 19.3 Roundworms (Phylum Nematoda) 11. Psrudocoel means "false body cavity." Why is this term applied to the body cavity of roundworms? 19.4 Joint-Lexged Animals (Phylum Arthropoda) Define sexual dimorphism, describe it in the crayfish,and list two other animals that exhibit this phenomenon. 12.

Explanation / Answer

8. The growth ridges found on the shells of bivalves occur as a result of restricted growth periods. These are formed as a result of deposition of calcium carbonate on the bivalves. After deposition occurs, there will be formation of a growth ring. This layer is laced down by the mantle. The unbo would form the first of the clam shells.

9. Bivalves from the other molluscan classes could be distinguished by the possession of a ventral muscular foot that aids movement named as the mantle. In other molluscs, the mantle which help in gaseous exchange.

19. Slugs do not have shells and are terrestrial.

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