Revisiting Hypostomus khimaera (Siluriformes: Loricariidae): the identity of a morphologically variable species

Abstract

Hypostomus khimaera, described from the upper rio Paraguai basin in Brazil, was reported to present some morphological variations in its original description, which allied to its relatively wide geographical distribution reinforced the need for a new assessment of its taxonomic status. Here, we analyzed a new robust set of material, composed by 636 specimens from several localities within the upper rio Paraguai basin, besides the material listed in the original description. From this, it was possible to better understand the limits of the species providing a more accurate diagnosis and a redescription for H. khimaera, which also brought some light to the limits of the H. cochliodon group itself. The species can be distinguished from its congeners by having the following features: (I) absence of a notch between the metapterygoid and hyomandibula, (II) acutely angled dentaries, with up to about 90°, (III) teeth with medial cusp ranging from villiform to shovel-shaped, (IV) opercle completely surrounded by a thick layer of skin, (V) a longitudinal dark stripe along middle portion of flanks, which is variably diffuse, and (VI) dark spots on at least one part of the body. Although morphological and color pattern differences have been found in different populations along the upper rio Paraguai basin, all examined specimens are herein considered to belong to H. khimaera, a decision based on both morphologic and molecular analyses. Additionally, an updated identification key for the Hypostomus species in the Brazilian portion of the upper rio Paraguai basin is also provided.

Keywords:
Armored catfish; Hypostomus cochliodon; Identification key; Rio Paraguai basin; Taxonomy