Understanding Heart Auricles in Animals

The question asks us to identify which of the given animals have a heart auricle that consists of a single chamber. The auricle, also known as the atrium, is a chamber in the heart that receives blood from the body or the lungs before it is pumped into the ventricle.

Heart Structure Overview

Different groups of animals have varying numbers of heart chambers. This structure is adapted to their physiological needs and how they obtain oxygen.

Heart in Cartilaginous Fishes

Cartilaginous fishes, such as sharks, rays, and chimaeras, belong to the class Chondrichthyes. They typically possess a two-chambered heart. This heart consists of:

• A single atrium (auricle)
• A single ventricle

In this simple circulatory system, deoxygenated blood enters the single atrium, moves into the single ventricle, and is then pumped to the gills for oxygenation before circulating through the rest of the body. Thus, cartilaginous fishes have a heart auricle composed of a single chamber.

Heart in Frogs

Frogs are amphibians (class Amphibia). Most adult amphibians have a three-chambered heart. This heart consists of:

• Two atria (right and left)
• One ventricle

The right atrium receives deoxygenated blood from the body, while the left atrium receives oxygenated blood from the lungs and skin. Both atria empty into a single ventricle, where some mixing of oxygenated and deoxygenated blood occurs. Therefore, frogs have two auricles, not one.

Heart in Crocodiles

Crocodiles are reptiles (class Reptilia). While most reptiles have a three-chambered heart with a partially divided ventricle, crocodiles are unique among reptiles in having a completely four-chambered heart. Their heart consists of:

• Two atria (right and left)
• Two ventricles (right and left)

This structure allows for complete separation of oxygenated and deoxygenated blood, similar to birds and mammals. The right atrium receives deoxygenated blood, and the left atrium receives oxygenated blood. Therefore, crocodiles have two auricles, not one.

Conclusion on Single Chambered Auricle

Based on the structure of the heart auricle (atrium) in each animal group:

• Cartilaginous fishes have one atrium (single chamber).
• Frogs have two atria (multiple chambers).
• Crocodiles have two atria (multiple chambers).

Therefore, among the given options, only cartilaginous fishes have a heart auricle that consists of a single chamber.