Cryptic lineages in Neotropical freshwaters: an integrative approach reveals a new species of Megalonema (Siluriformes: Pimelodidae) from the upper Paraná River basin

Abstract

Abstract A new species, previously identified as Megalonema platanum, is described as Megalonema tinga from the Paranapanema River basin, based on morphological (morphometry and meristic) and DNA-barcoding analyses. Body proportions based on 28 measurements in 25 specimens of M. tinga and 10 of M. platanum showed a high degree of overlap. However, an analysis of 15 measurements of M. tinga (n = 28) and M. platanum (n = 13), using sheared principal components analysis, applied to the covariance matrix of logarithmized morphometric variables, supported differentiation between the two species. The meristic analysis showed that M. tinga has fewer gill rakers in the first ceratobranchial (six to eight) than M. platanum (nine to 11), a character ontogenetically stable. COI-based species delimitation (ASAP, mPTP, and GMYC) also indicated species-level differentiation, separating supposed M. platanum into two groups, one of which is the new species. The new species is also distinguished from other Megalonema species by morphological or molecular features.