The genus Tometes Valenciennes, 1850 was originally described for the typespecies
T. trilobatus, by presenting incisiform and bi- tricuspid teeth. However,
the genus was synonymized with Myleus Müller and Troschell, 1844 for
approximately a century and a half until being revalidated with an addition of
two new species descriptions, T. lebaili and T. makue. This study presents a
taxonomic review of Tometes from Guyana Shield where the three nominal
species are recognized as valid and here were re-described, also a new
species from Trombetas basin was described, increasing the diversity and
distribution of genus. Among the main characteristics of diagnosis were
observed: T. trilobatus is distinguishes from its congeners by having dentary
and premaxillary teeth with the central cusp with rounded edge (vs. teeth with
the central cusp or principal cusp with sharp edge). T. lebaili differs from others
Tometes by having mouth oblique dorsally directed (vs. terminal mouth). T.
makue is different by having a few spines on the serrae prepelvic, always
between 0 and 9 spines (vs. over 9 spines). Already the new species is
distinguished by the neurocranium with a slight concavity at the level of the
epiphyseal bar, and also by having scales of irregular size (vs. dorsal profile of
the neurocranium without a slight concavity, and scales of regular size). All
species of Tometes are strictly rheophilic, and occur exclusively in the rapids of
shield rivers, complex and fragile biotopes that are threatened by anthropogenic
activities. The conclusions reached by this study highlight the urgent challenge
to understand more fully existing species/habitat relationships.
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