What type of circulatory system do arthropods possess?

Arthropods possess an open circulatory system, which is characterized by the absence of blood vessels that completely contain the circulatory fluid. Instead, the blood (referred to as hemolymph) flows freely within a hemocoel, a body cavity that bathes the organs directly. This system allows for efficient nutrient and waste transport but relies on the movement of the organism to help circulate the hemolymph throughout its body.

In contrast to a closed circulatory system, where blood is confined within vessels, an open circulatory system is generally less efficient in terms of transporting oxygen and nutrients, yet it suits the lifestyle and metabolic demands of arthropods. Their activity levels and physiological needs are adapted to this more primitive circulatory system, which is often sufficient given their size and habitat.

Closed circulatory systems, found in vertebrates, have distinct vessels for blood that provide greater control and efficiency in routing blood to various tissues, while single and double circulatory systems refer specifically to certain types of closed systems in other organisms, which do not apply to arthropods.