You are confronted with two worms that, on first glance, appear to be very similar. Upon closer examination, however, you note one difference that allows you to identify one specimen as an earthworm and the other as a roundworm. That key characteristic is: A. The presence of a gastrovascular cavity B. The presence of a body cavity C. The presence of a muscle layer around the digestive tract D. The absence of a specialized gas exchange surface E. None of the characteristics listed above would allow an earthworm to be distinguished from a roundworm

Strepsirrhines have a special trait resulting from the crowding of multiple lower incisors and canines called a A. Tooth comb B. Bilophodont C. Diastema D. Two-ridge tooth

Modern sponges produce microscopic spicules (right) to deter predation but, as the earliest animals, they existed before any predators evolved; how might biologists interpret this observation?   A. Spicules were probably absent in the earliest sponges and evolved later as predation began. B. Spicules performed other tasks in early sponges, possibly structural support, and were later modified for defense. C. Spicules were present in some sponge species and absent in others; predation became a selection pressure that eliminated some species entirely. D. All of the above are valid hypotheses.

Which of the following will increase the rate of O2 uptake by a lobster? A. Increasing the partial pressure of O₂ in the hemolymph (i.e. blood) of the lobster B. Increasing the flow of water over the gill (i.e. increasing ventilation) C. Increasing the thickness (i.e. the hemolymph-to-water distance) of the gill D. Increasing the surface area of the scaphognathite E. All of the above