One of your closest fish relatives is the coelacanth. Where is its equivalent to your forearm?

Question

A.  The claspers
B.  The pectoral fin lobe
C.  The operculum
D.  The gill arch extensions
E.  The pelvic fin lobe

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

Gather Content
· What do you already know about the coelacanths?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  The pectoral fin lobe

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the coelacanths.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.

Gather Content
· What do you already know about the coelacanths?
        o The two major groups of bony fish differ in the structure of their fins: the ray-finned fishes and the lobe-finned fishes.
        o In ray-finned fishes, the internal skeleton of the fin is composed of parallel bony rays that support and stiffen each fin. There are no muscles within the fins -- they are moved by muscles within the body.
        o By contrast, coelacanths have paired fins that consist of a long fleshy muscular lobe supported by a central core of bones that form fully articulated joints with one another. There are bony rays only at the tips of each lobed fin. Muscles within each lobe can move the fin rays independently.
        o Lobe-finned fish evolved 390 mya, shortly after the first bony fishes appeared. Only eight species survive today, two species of coelacanth (subclass Actinistia) and six species of lungfish (subclass Dipnoi). Although rare today, lobe-finned fishes played an important part in the evolutionary story of vertebrates because it was a coelacanth that crawled out of water and colonized land, giving rise to the first amphibians. Lungfish are more closely related to tetrapods (legged vertebrates) than they are to coelacanths, thus making the Sarcopterygii a paraphyletic group.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The coelacanth’s lobed fins represent the limbs that evolved into the amphibian legs.
        o So the pectoral lobe fins (toward the front of the coelacanth’s body) would be homologous to your forearms.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that the coelacanth lobe fins are homologous to your arms and legs?