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They breathe through a series of spiracles—external openings connected to a tracheal system that transports oxygen directly to cells, bypassing the need for an external respiratory surface like gills or a lung. This system is efficient for their sedentary lifestyle and confined terrestrial niches.
Circulatory System
Their circulatory system comprises a body cavity known as a hemocoel, filled with hemolymph—a pigmentless, blood-like fluid that transports nutrients and hormones but does not carry oxygen. Embedded within the hemocoel are amoebocytes, which fight infections and play roles in reproduction, and nephrocytes that detoxify by absorbing toxins and ferrying wastes to the excretory organs.