Crustaceans and arachnids possess paired excretory organs (maxillary, antennal, or coxal glands) that open at the bases of certain appendages. Myriapods, insects, and some arachnids, such as spiders and mites, possess another type of excretory organ, Malpighian tubules, which open into the intestine. Thus in these animals both excretory and digestive wastes exit from the anus Spiders common in warm dry regions, usually terrestrial (Subphylum Chelicerata; Class Arachnida) and insects, most diverse and abundant of all groups of arthropods (Subphylum Haxapoda, Class Insecta) have independently evolved a unique excretory system of Malpighian tubules, which work in conjunction with specialized resorptive cells in the intestinal epithelium. Potassium and other solutes and waste materials are secreted into the tubules, which drain the fluid, or “urine,” into the intestine. Resorptive cells recapture most potassium and water, leaving behind such wastes as uric acid. This recycling of water and potassium allows species living in dry environments to conserve body fluids by producing a nearly dry mixture of urine and feces. Many spiders also have coxal glands, which are modified nephridia that open at the coxa or base, of the first and third walking legs.
(Chilopoda – centipedes; Diplopoda – millipedes; Pauropods – pauropods; Symphyla – symphylans) Excretion is usually by Malpighian tubules, but these have evolved independently of Malpighian tubules found in Chelicerata.
In Class Chilopoda (centipedes), two pairs of Malpighian tubules empty into the hind part of the intestine.
(mainly marine however there are many freshwater and a few terrestrial species)
Excretory organs of adult crustaceans are a pair of tubular structures located in the ventral part of their head anterior to the esophagus. They are called antennal glands or maxillary glands, depending on whether they open at the base of the antennae or at the base of second maxillae. A few adult crustaceans have both. Excretory organs of decapods are antennal glands also called green glands in this group. Crustaceans do not have Malpighian tubules, the excretory organs of spiders and insects. The end sac of the antennal gland consists of a small vesicle (saccule) and a spongy mass called a labyrinth. The labyrinth connects by an excretory tubule to a dorsal bladder, which opens to the exterior by a pore on the ventral surface of a basal antennal segment. Hydrostatic pressure within the...