The trichomycterid catfish Listrura menezesi, new species, is described from a flooded area adjacent to Rio das Panelas, Rio São João basin, Cachoeiras de Macacu municipality, Rio de Janeiro State, Brazil. It represents a most valuable remnant of Atlantic Forest biome that still resists the devastation of Brazilian coastlands. Listrura menezesi can be distinguished from its congeners, except L. boticario and L. depinnai, by the absence of a dorsal fin. It mainly differs from L. boticario and L. depinnai by a continuous midlateral dark stripe along the entire body (vs. discontinuous) and a longitudinal row of irregular dots along the dorsal limit of the abdomen extending for nearly the entire body (vs. only on the posterior half of the body in L. boticario and not forming a distinct row in L. depinnai). Although the new species shares with L. boticario and L. depinnai the absence of dorsal fin, recent phylogenetic analyses show a close relationship between L. menezesi and L. macaensis, the latter having a dorsal fin. A putative apomorphic condition for this clade is presented: the abrupt widening on the mesethmoid axis starting posteriorly on the horizontal through the middle region of the autopalatine (vs. anteriorly, on the horizontal through the anterior region of the autopalatine). Listrura menezesi comes as an addition to the ichthyofauna of the Rio São João drainage, a region extensively sampled for the past 20 years and supposedly well known. This paper also highlights the vulnerability of this species and the possibility of its disappearance in the near future.
Keywords: Atlantic rain forest; Rio São João basin; catfish; taxonomy.
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