Editing Chelicerata (section)

===Excretion===
Horseshoe crabs convert [[nitrogen]]ous wastes to [[ammonia]] and dump it via their gills, and excrete other wastes as [[feces]] via the [[anus]]. They also have [[nephridia]] ("little kidneys"), which extract other wastes for excretion as [[urine]].<ref name="RuppertFoxBarnes2004Xiphosura" /> Ammonia is so toxic that it must be diluted rapidly with large quantities of water.<ref name="RuppertFoxBarnes2004P529To530">{{harvnb|Ruppert|Fox|Barnes|2004|pp=529–530}}</ref> Most terrestrial chelicerates cannot afford to use so much water and therefore convert nitrogenous wastes to other chemicals, which they excrete as dry matter. Extraction is by various combinations of nephridia and [[Malpighian tubules]]. The tubules filter wastes out of the blood and dump them into the hindgut as solids, a system that has evolved [[convergent evolution|independently]] in [[insect]]s and several groups of [[arachnid]]s.<ref name="RuppertFoxBarnes2004ArachnidaGen" />