Side (engorged) and ventral views of Vandellia cirrhosa The Trichomyteridae comprise a family of over 40 genera and about 180 species of small, nearly transparent catfish termed "pencil catfish" or "parasitic catfish." Most are only a few centimeters in length and many inhabit sandy or muddy bottoms where they feed on a variety of protozoa, rotifers, and insect larvae. Some species, however, enter the gill chambers of other fish, erect a spine to hold them in place, and ingest blood for a minute or two from the gill filaments. Rarely, in the Amazon, members of the genus Vandellia (and perhaps a few closely related species in other genera) accidently enter the urethra, vagina, or rectal orifices of humans. The species most commonly reported as intraurethral is Vandellia cirrhosa ("candiru," "carnero," "canero,", or "vampire catfish"). The exact reason why this fish might accidently enter a body orifice is unknown, although the presence of ammonia or urea in the water has been a popular hypothesis. Evidence by Spotte et al. (2001, Environ. Biol. Fishes, 60: 459-464) suggests this hypothesis may not be true. Surgical removal is the primary method of therapy.