Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes.

A new species of Pimelodella is described from several right-bank tributaries of the Rio Madeira basin in Amazonas and Rondônia states, Brazil. The new species differs from all congeners by the supraoccipital process not reaching the anterior nuchal plate, 43-45 total vertebrae, maxillary barbels reaching between adpressed anal-fin terminus and caudal-fin origin, epiphyseal branch of supraorbital laterosensory canal emerging as two distantly-positioned pores and a conspicuous black mark at distal third of dorsal fin, between dorsal-fin spine and third branched ray. A detailed description of the cephalic laterosensory system of the new species is provided and contrasted with other Siluriformes and Ostariophysi. A discussion regarding homology of the catfish upper pectoral girdle bones is offered in light of modifications of the postotic and supratemporal lateral-line canals. Based on the placement of the pterotic branch of the postotic canal, it is concluded that the extrascapula is fused to the pterotic in Siluriformes. Results presented herein offer an example of how lateral-line morphology can be used as a compelling source of evidence to help determine homology of cranial and upper pectoral girdle bones.

A new species of Pimelodella (Siluriformes: Heptapteridae) from the Guiana Shield, Brazil.

A new species of Pimelodella is described from the Rio Ipitinga, Rio Jari basin, a left bank tributary of the Rio Amazonas in Brazil. The new species is diagnosed from all congeners by having a dark oval mark on the humeral region. It also differs from all congeners by a unique set of characters, including the presence of 47 to 49 total vertebrae, unpigmented areas dorsally and ventrally adjacent to the dark midlateral stripe, and maxillary barbels reaching at least to vertical through caudal fin insertion. Faunal similarities between the southern part of the eastern Guiana Shield and coastal drainages in the Guianas and Suriname are discussed.

A new Brachyrhamdia (Siluriformes: Heptapteridae) from Rio Japurá basin, Brazil, with comments on its phylogenetic affinities, biogeography and mimicry in the genus.

Brachyrhamdia thayeria is herein described as a new heptapterid species from Rio Japuré, a left margin tributary of the Rio Solimões, Amazonas basin, Brazil. The new species is diagnosed from all its congeners by having a putative autapomorphy: dark oblique stripe across the caudal peduncle, originating below the anterior half of adipose fin and ending at base of rays of ventral caudal-fin lobe. Brachyrhamdia thayeria is considered closely related to B. imitator and B. rambarrani with which it shares a low vertebral number and absence of lateral stripe along trunk. The new species shares exclusively with B. rambarrani the presence of a dark conspicuous bar along the dorsolateral region of trunk, a putative synapomorphy. Brachyrhamdia are distributed in lowland regions of northern South America where they inhabit small streams with running waters. The new species appears to have a mimetic association with the syntopic callichthyid Corydoras arcuatus. Herein, we argue in favor of the hypothesis that the interaction between species of Brachyrhamdia and Pimelodella or Corydoras is Müllerian mimicry.