While on an intersession course in tropical ecology, Kris pulls a large, snakelike organism from a burrow (the class was granted a collecting permit). The 1-m-long organism has smooth skin, which appears to be segmented. It has two tiny eyes that are hard to see because they seem to be covered by skin. Kris brings it back to the lab at the field station, where it is a source of puzzlement to the class. Kris says that it is a giant oligochaete worm; Shaun suggests it is a legless amphibian; Kelly proposes it belongs to a snake species that is purely fossorial (lives in a burrow).
The class decided to humanely euthanize the organism and subsequently dissect it. Having decided that it was probably not a reptile, two of their original hypotheses regarding its identity remained. Which of the following, if observed, should help them arrive at a conclusive answer?
A) presence of a closed circulatory system
B) presence of moist, highly vascularized skin
C) presence of lungs
D) presence of a nerve cord
E) presence of a digestive system with two openings
Answer: C
The organism was found to have two lungs, but the left lung was much smaller than the right lung. Kelly added that the herpetology instructor had said that in most snakes, the same condition exists. If the size difference between the lungs in this organism is not a shared ancestral characteristic with its occurrence in snakes, then its existence in this organism is explained as which of the following?
1. a result of convergent evolution
2. an example of homologous structures
3. a similar adaptation to a shared lifestyle or body plan
4. a result of having identical Hox genes
5. a homoplasy
A) 3 only
B) 1 and 5
C) 1, 3, and 5
D) 2, 3, and 5
E) 3, 4, and 5
Answer: C
The adaptation of the body shape of snakes has resulted in one of their lungs becoming vestigial. Another adaptation (to a fossorial lifestyle) is snakes' absence of limbs. If the "mystery organism" has also become adapted to a fossorial lifestyle, though its ancestors moved about on the surface, then which structures should one expect to find upon dissecting the organism?
1. reduced or absent pelvic and/or pectoral girdles
2. metanephridia
3. hydrostatic skeleton
A) 1 only
B) 1 and 2
C) 1 and 3
D) 2 and 3
E) 1, 2, and 3
Answer: A
Which one of these, if found, should clear up any remaining doubt as to the identity of the organism?
A) vestigial pelvic girdle
B) blood vessels carrying oxygenated blood from both the skin and the functional lung to the heart
C) closed circulatory system
D) ability to produce toxins from glands located on the skin, or that empty into the mouth
E) two-chambered heart
Answer: B
