The heart is an important organ in the animal's body and is responsible for transporting blood throughout the body to provide oxygen and nutrients to the body. However, in nature, there are also animals that do not have hearts. How do these animals survive?How does their circulatory system work?
Invertebrates
Most invertebrates do not have hearts. Their circulatory system is open, and blood flows into the body cavities. For example, the blood of insects is called hemolymph, which flows into body cavities and then back up to the heart through blood vessels and the walls of body cavities.
Cephalopods
Cephalopods are the only invertebrates that possess a closed circulatory system. Their heart is made up of three atria and two ventricles that are responsible for pumping blood throughout the body. However, cephalopod hearts are not as complex as vertebrate hearts. Their hearts do not have valves, and the flow of blood is mainly driven by the contraction and relaxation of the heart.
Annelids
The circulatory system of annelids is also relatively simple. Their heart is made up of five arterial arches that are responsible for pumping blood throughout the body. The blood of annelids is also relatively simple, consisting mainly of water and hemoglobin.
Vertebrates
The circulatory system of vertebrates is closed, and blood does not flow into the body cavities. The heart of a vertebrate animal is made up of four heart chambers that are responsible for transporting blood throughout the body. The heart of vertebrates is more complex and has valves to control the flow of blood.
Vertebrates without hearts
While most vertebrates have hearts, there are some exceptions. For example, hagfish and sea slugs are two types of vertebrates that do not have hearts.
Hagfish are fish that live in the deep sea, and their hearts degenerate during embryonic development. The hagfish's circulatory system consists of a network of blood vessels, and the flow of blood is mainly driven by muscle contractions.
Sea slugs are a mollusk that also has a degenerated heart after becoming an adult. The circulatory system of the sea slug consists of a network of blood vessels, and the flow of blood is mainly driven by muscle contraction and contraction of the walls of the body cavity.
Conclusion
In nature, there are a wide variety of animals that vary in morphology and physiology. Animals without hearts are also a peculiar being, and their circulatory system also has a certain uniqueness.
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