Trigonomonas (try-go-know-moan-0ass) diplomonad flagellate, a group best known because it includes Giardia, an organism relevant to public health (it causes diarrhoea) and because of its relevance to early cell evolution. Trepomonas is less common than Hexamita, and differs because there are only three flagella in each group - one of each group is long, the others are short and none trail behind the cell. Tends to move in a series of sudden turns interspersed by slow rotations. Differential interference contrast.