A new species of Diapoma (Characiformes, Characidae, Stevardiinae) from the Rio Paraná basin, with an identification key to the species of the genus

Abstract

Diapoma nandi is described from the Piray-Miní stream, a tributary of the Rio Paraná in Argentina. It is characterized among the Stevardiinae by having a terminal mouth, two unbranched and eight branched dorsal-fin rays, one unbranched and six branched pelvic-fin rays and the absence of a caudal-fin organ and is distinguished from all congeners by the following combination of characters: unmodified scales on the lower caudal-fin lobe, lack of enlarged opercle and subopercle, incomplete lateral line, hyaline adipose fin, anal-fin distal border straight or slightly convex in adult males, large tricuspid teeth on anterior region of the dentary, distal arrangements of the anal-fin bony hooks in adult males, middle caudal-fin rays lacking large round blotch and several morphometric variables associated with body shape. Additionally, we conducted a morphometric comparison focused on the congeners that co-occur in the Paraná basin.

Phylogenetic relationships of a new genus and species of stevardiine fish (Characiformes: Characidae: Stevardiinae) from the Río Amazonas basin, Peru

“…with Diapoma as the only exception (Thomaz et al, 2015;Vanegas-Ríos, Azpelicueta, & Malabarba, 2018). However, and as found in different phylogenetic studies using morphological data, the mere presence of the hypertrophied caudal-fin squamation does not support a monophyletic group (Ferreira, Menezes, & Quagio-Grassioto, 2011;Menezes & Weitzman, 2009;Mirande, 2018;Vanegas-Ríos, 2018;Weitzman et al, 2005).…”

“…In addition to that squamation, all those genera can be partly or exclusively diagnosed or defined by other remarkable features associated with bony hooks, caudal muscles, and spur‐shaped structures (Arcila, Vari, & Menezes, ; Menezes & Weitzman, ; Vanegas‐Ríos, ; Weitzman & Fink, ; Weitzman & Menezes, ; Weitzman, Menezes, Evers, & Burns, ; Zarske, ). Most characters related to the terminal caudal‐fin squamation have played a crucial role in defining stable generic limits among the stevardiines, especially in those species with modified squamation on the lower caudal‐fin lobe (Arcila et al, ; Deprá, Graça, Pavanelli, Avelino, & Oliveira, ; Menezes, Weitzman, & Burns, ; Vanegas‐Ríos, , ; Weitzman & Fink, ; Weitzman, Fink, Machado‐Allison, & Royero, ;Weitzman & Malabarba, ; Weitzman & Thomerson, ); with Diapoma as the only exception (Thomaz et al, ; Vanegas‐Ríos, Azpelicueta, & Malabarba, ). However, and as found in different phylogenetic studies using morphological data, the mere presence of the hypertrophied caudal‐fin squamation does not support a monophyletic group (Ferreira, Menezes, & Quagio‐Grassioto, ; Menezes & Weitzman, ; Mirande, ; Vanegas‐Ríos, ; Weitzman et al, ).…”

On the lectotype designation of Bryconamericus rubropictus (Berg) (Characiformes, Characidae, Stevardiinae)

“…Measurements and other counts were taken based on Fink and Weitzman (1974), with the addition of the anal‐fin lobe length and the distance between the dorsal‐ and pectoral‐fin origins, following Vanegas‐Ríos et al (2018). Measurements were taken point to point using digital calipers under a stereomicroscope and expressed as percentages of standard length ( L S ) or head length ( L H ) for units of the head.…”