A New Species of Chaetostoma (Siluriformes: Loricariidae) Expands the Distribution of Rubbernose Plecos Eastward into the Lower Amazon Basin of Brazil

A new species of the rubbernose pleco genus Chaetostoma is described from the Maicuru and Seiko Rivers, a northern tributary of the lower Amazon River and a tributary of the lower Xingu River, respectively, both in Para´ State, Brazil. The new species is diagnosed from all congeners, except members of the Chaetostoma anale species group, by having an enlarged second unbranched anal-fin ray with posterior paired dermal flaps. Additionally, the new species is distinguished from its only other currently recognized congeners from rivers draining the Guiana Shield (C. jegui and C. vasquezi) by having a smaller opercle and a supraoccipital excrescence undeveloped, comprising a simple skin area present in juveniles and absent in adults. A revised multi-locus phylogeny for the species of Chaetostoma is presented, and the Chaetostoma anale species group is discussed and rearranged.