Summary
Amazonadistoma negrensis n. gen., n. sp. (Trematoda : Digenea : Gorgoderidae) is described from an Amazonian fish called the "sarapó-de-bico", Gymnorhamphichthys hypostomus Ellis (Gymnotoidea : Rhamphichthyidae). The new genus is similar to Phyllodistomum from which it differs in having: a thick and muscular hindbody with lateral corrugations; ceca with branches; extracecal uterine loops in the hindbody and a sinuous seminal vesicle. The new form also inhabits the intestine of the host and not the urinary bladder. A. negrensis is entirely black in color, and could only be studied by destaining for 5 weeks in 1% ammonia solution. This is the first report of a black trematode, and the color is believed to be caused by fungal invasion of the living worms. A. negrensis also has microvilli projecting from the intestinal epithelium, as has been reported for some Paramphistomoidea. The presence of microvilli is considered to be a primitive trait. A. negrensis has a body averaging 2,4 x 5,6 mm. and eggs measuring 23x30 µm.