1 The kidneys are used to remove excess water and ions from the blood. 2  These are then expelled as urine. 3  The kidneys perform a vital role in homeostatic regulation in mammals, removing excess water, salt, and urea from the blood.
Ectoparasites Parasites that live on the outside of the host, either on the skin or the outgrowths of the skin, are called ectoparasites. They are directly transmitted between hosts.
Parasites are generally harmful to their hosts, although the damage they do ranges widely from minor inconvenience to debilitating or fatal disease. â A parasite that lives or feeds on the outer surface of the host's body, such as a louse, tick, or leech, is called an ectoparasite.