We herein present the first taxonomic account on the genera
Amblyosyllis,
Brevicirrosyllis,
Eusyllis and
Opisthodonta from Brazilian waters, with the description of
Eusyllis nonatoi sp. nov. The new species is characterized by having transverse dark stripes on dorsum, unidentate, relatively short falciger blades with inverted dorso-ventral gradation in length, and distally rounded to inconspicuously bifid dorsal simple chaetae. In addition, the description of
Eusyllis liniata comb. nov., from Peru, originally described as belonging to
Odontosyllis, is also provided. Finally, we amend the description of
Opisthodonta russelli, originally described from anterior fragments only.
