a flattened, heart-shaped motile flagellated organism (10-20 mcm in length) with eight flagella; it attaches itself to the intestinal mucosa by means of a pair of sucking organs; in humans it is usually asymptomatic except in cases of heavy infection, when it may interfere with absorption of fats and produce flatulence, steatorrhea, bloating, and acute discomfort; it is the common species of Giardia in humans but is also found in pigs, dogs, cats and other mammals. In dogs and cats, it is commonly associated with bloating, flatulence, tenesmus, weight loss, and malodorous mucoid or bloody soft frothy voluminous stools; can have severe clinical course in young, sick or immunocompromised hosts. Chronic infestations may lead to debilitation. May be asymptomatic. SYN: Giardia lamblia.