Coxal gland

Excretory organ in some arthropods

The coxal gland is an excretory organ found in certain arthropods, including some crustaceans and arachnids. These glands play a crucial role in the regulation of water and ion balance within the organism, functioning similarly to the kidneys in vertebrates.

Structure

Coxal gland structure

The coxal gland is typically composed of a series of tubules that are involved in the filtration and excretion of waste products. The gland is named for its location near the coxa, or the base segment of the leg, in these arthropods. The structure of the coxal gland can vary significantly among different species, but it generally includes a sac-like end sac, a long coiled tubule, and a terminal bladder that opens to the exterior.

End Sac

The end sac is the initial site of filtration. It collects hemolymph, the fluid equivalent of blood in arthropods, from the surrounding tissues. The walls of the end sac are often thin and permeable, allowing for the selective passage of ions and small molecules.

Tubule

The tubule is responsible for the reabsorption of useful substances such as ions and water. It is often highly coiled, increasing the surface area for reabsorption. The tubule's lining is composed of specialized cells that actively transport ions back into the hemolymph, conserving essential nutrients and maintaining osmotic balance.

Bladder

The bladder serves as a storage area for the excretory products before they are expelled from the body. It connects to the exterior through a duct that opens near the base of the leg, allowing the organism to excrete waste efficiently.

Function

The primary function of the coxal gland is to maintain osmotic balance and remove metabolic waste products from the body. By filtering hemolymph, reabsorbing necessary ions, and excreting waste, the coxal gland helps regulate the internal environment of the organism, ensuring homeostasis.

Variations Among Species

Coxal glands are found in various arthropods, but their structure and function can differ significantly. In some crustaceans, such as crabs and lobsters, the coxal glands are well-developed and play a major role in excretion. In arachnids, such as spiders and scorpions, the coxal glands are often reduced or modified, sometimes working in conjunction with other excretory organs like Malpighian tubules.

Evolutionary Significance

The presence of coxal glands in diverse arthropod groups suggests an evolutionary adaptation to terrestrial and aquatic environments. These glands allow arthropods to efficiently manage water and ion balance, which is crucial for survival in varying habitats.

Related Pages

• Excretory system
• Arthropod anatomy
• Malpighian tubule system