Clams and other bivalves typically have:

Clams and other bivalves typically have:
  a. dermal gills.
  b. gills adapted for trapping food.
  c. an operculum.
  d. book lungs.
  e. swim bladders

Question 2

The countercurrent exchange system found in fish gills maximizes gas exchange efficiency by:
  a. producing rapid water flows across the gill surface.
  b. allowing water and blood to come in direct contact to maximize oxygen exchange.
  c. having a high concentration gradient of oxygen at the start of the capillaries.
  d. maintaining a high concentration gradient of oxygen along the entire length of capillaries.
  e. decreasing the oxygen content of the blood leaving the gill filaments