Practice question

Coxal glands represent sac-like excretory organs opening near coxae of walking legs in arachnids such as spiders, scorpions and also in some crustaceans like Limulus horseshoe crab, suggesting ancestral chelicerate trait. Organization includes end sac for ultrafiltration of hemolymph, labyrinth of convoluted tubule for reabsorption of salts and water, and straight duct leading to external coxal pore. Functionally similar to nephridium of annelids. In insects coxal glands reduced, replaced by Malpighian tubules; myriapods retain one pair but primarily rely on Malpighian tubules. Coxal glands thus supplement water balance in terrestrial arachnids and marine chelicerates.