Tunga bossii new species of tungid sand flea belonging to the caecata group is described with illustrations of the adult female, parasitizing the wild rodent Delomys dorsalis (Hensel) from Brazilian Atlantic Forest. Tunga bossii differs from the ten other known species of Tunginae by the size of the first segment of the maxillary palp and the presence of two bristles at the base of the maxilla. Tunga bossii also can be differentiated from other species of the T. caecata group by the eye morphology. A key to the adult species and neosomes of the genus Tunga also is included.