A student dissecting am animal specimen discovered that it had two auricle and on ventricle. The animal is likely to a/an

Analyze the question: The specimen's heart has two auricles (atria) and one ventricle, which makes it a three-chambered heart. We need to match this to the right class of animal.

Concept: heart structure in vertebrates

| Animal group | Heart chambers | |---|---| | Fish | 2 chambers (1 auricle, 1 ventricle) | | Amphibians (e.g., frog, toad) | 3 chambers (2 auricles, 1 ventricle) | | Reptiles | 3 chambers (2 auricles, 1 ventricle, usually partly divided) | | Birds and mammals | 4 chambers (2 auricles, 2 ventricles) |

Step-by-step solution:

1. Fish have only one auricle and one ventricle, so A is wrong.
2. Birds have a four-chambered heart with two ventricles, so D is wrong.
3. Amphibians and reptiles both have two auricles. The difference is in the ventricle: • Amphibians have a single undivided ventricle, so oxygenated and deoxygenated blood mix a little. • Reptiles have a ventricle that is partly divided by an incomplete septum (crocodiles are the exception, with four chambers).
4. The question says "one ventricle", which matches the amphibian heart (like the frog's) exactly. This is the standard textbook answer.

Answer: C (amphibian)

Exam tip: Remember the chamber count as 2-3-4: Fish = 2, Amphibians and Reptiles = 3, Birds and Mammals = 4. If the question says "two auricles and one ventricle" with amphibian and reptile both listed, choose amphibian when the options say "one ventricle" and reptile only when they mention a "partially divided ventricle".