mycterids generally are equipped with interopercles
and opercles that support odontodes. They can
evert these odontodes for protection and to provide
friction when climbing waterfalls. The candirus are
often described as the only parasitic vertebrates
(Gudger 1930) and are in two subfamilies. The
Stegophilinae feed on mucus and scales of other
fi shes, and the Vandeliinae feed on blood of other
fi shes. Fernández and Schaefer (2009) found that
parasitism arose only once in the trichomycterids.
Vandellines swim into the gills of other fi shes and
use a uniquely derived median upper jaw bone to
pierce the dorsal or ventral aorta and rapidly fi ll
themselves with blood (Spotte et al. 2001; Spotte
2002; Zuanon and Sazima 2004). The fi shes then
drink the blood and drop out of the fi sh when they
get their fi ll. They are often collected engorged
with blood in sandy streams (Figure 5). Although
there are not that many species of hematophagous
trichomycterids, legends of the candiru dominate
our thoughts on this group of fi shes because they
have been known to mistake the human urethra for
fi sh gills (Gudger 1930; Vezhaventhan and Jeyaraman
2007; Zuanon and Sazima 2004). The result is
damaging to both fi sh and human.