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Difficulty: MediumVertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

During a anatomical examination of the circulatory system in adult ectothermic vertebrates, a biologist observes a heart containing two auricles (atria) and a single ventricle that is partially divided by an incomplete septum. Which class of vertebrates possesses this cardiac architecture?

  1. ReptiliaAnswer
  2. B
    Amphibia
  3. C
    Pisces
  4. D
    Aves

Answer

Reptilia
Members of the class Reptilia (such as lizards, snakes, and turtles) feature a three-chambered heart composed of two auricles and a single ventricle partially divided internally by an incomplete septum, which minimizes the mixing of oxygenated and deoxygenated blood streams.

Step-by-Step Solution

1
Identify the key anatomical features described in the stem.
The heart has two auricles and one ventricle with an incomplete partition (septum).
This structural pattern determines the evolutionary stage of the vertebrate circulatory system.
2
Compare heart chamber configurations across poikilothermic vertebrate classes.
Pisces have 2 chambers (1 auricle, 1 ventricle); Amphibia have 3 chambers (2 auricles, 1 undivided ventricle); Reptilia have 3 chambers (2 auricles, 1 partially divided ventricle).
The partial ventricular septum is a key evolutionary adaptation in non-crocodilian reptiles that reduces mixing of oxygenated and deoxygenated blood.

Key Concept

Cardiac anatomical modifications across poikilothermic vertebrate classes
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Topics

Vertebrates: Poikilothermic Classes (Pisces, Amphibia, Reptilia)

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