Zooplankton, tiny animals adapted to an existence in the ocean, have evolved clever mechanisms for obtaining their food, miniscule phytoplankton (plant plankton). A very specialized feeding adaptation in zooplankton is that of the tadpolelike appendicularian who lives in a walnut-sized (or smaller) balloon of mucus equipped with filters that capture and concentrate phytoplankton. The balloon, a transparent structure that varies in design according to the type of appendicularian inhabiting it, also protects the animal and helps to keep it afloat. Water containing phytoplankton is pumped by the appendicularian's muscular tail into the balloon's incurrent filters. passes through the feeding filter where the appendicularian sucks the food into its mouth. and then goes through an exit passage. Found in all the oceans of the world, including the Arctic Ocean, appendicularians tend to remain near the water's surface where the density of phytoplankton is greatest.

17. It can be inferred from the passage that which of the following is true of appendicularians?

(A) They are exclusively carnivorous.
(B) They have more than one method of obtaining food.
(C) They can tolerate frigid water.
(D) They can disguise themselves by secreting mucus.
(E) They are more sensitive to light than are other zooplankton.




18. The author is primarily concerned with

(A) explaining how appendicularians obtain food
(B) examining the flotation methods of' appendicularians
(C) mapping the distribution of appendicularians around the world
(D) describing how appendicularians differ from other zooplankton
(E) comparing the various types of balloons formed by appendicularians




19. According to the passage, all of the following are descriptive of appendicularians EXCEPT

(A) tailed
(B) vegetarian
(C) small-sized
(D) single-celled
(F) ocean-dwelling




20. The passage suggests that appendicularians tend to remain in surface waters because they

(A) prefer the warmer water near the surface
(B) are unable to secrete mucus at the lower levels of the ocean
(C) use the contrast of light and shadow at the surface to hide from predators
(D) live in balloons that cannot withstand the water pressure deeper in the ocean
(E) eat food that grows more profusely near the surface