cheiracanthium punctorium, displaying fangs
uniquely among chelicerates, final sections of spiders chelicerae fangs, , great majority of spiders can use them inject venom prey venom glands in roots of chelicerae. families uloboridae , holarchaeidae, , liphistiidae spiders, have lost venom glands, , kill prey silk instead. arachnids, including scorpions, spiders have narrow gut can cope liquid food , spiders have 2 sets of filters keep solids out. use 1 of 2 different systems of external digestion. pump digestive enzymes midgut prey , suck liquified tissues of prey gut, leaving behind empty husk of prey. others grind prey pulp using chelicerae , bases of pedipalps, while flooding enzymes; in these species, chelicerae , bases of pedipalps form preoral cavity holds food processing.
the stomach in cephalothorax acts pump sends food deeper digestive system. mid gut bears many digestive ceca, compartments no other exit, extract nutrients food; in abdomen, dominated digestive system, few found in cephalothorax.
most spiders convert nitrogenous waste products uric acid, can excreted dry material. malphigian tubules ( little tubes ) extract these wastes blood in hemocoel , dump them cloacal chamber, expelled through anus. production of uric acid , removal via malphigian tubules water-conserving feature has evolved independently in several arthropod lineages can live far away water, example tubules of insects , arachnids develop different parts of embryo. however, few primitive spiders, sub-order mesothelae , infra-order mygalomorphae, retain ancestral arthropod nephridia ( little kidneys ), use large amounts of water excrete nitrogenous waste products ammonia.
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