Marine Crabs Have Internal Gills Covered by an Exoskeleton, And

Multiple Choice

Marine crabs have internal gills covered by an exoskeleton, and, because their whole body is covered by exoskeleton, they cannot expand their body enough to generate much negative pressure within the gill chambers to draw water in over their gills. Which of the following would serve to increase the efficiency of gas exchange by marine crabs?

A) a countercurrent exchange system
B) oxygen- carrying molecules in the blood
C) movement of limbs or other structures to create a current over the gills
D) all of the above
E) only B and C