Deconstructing an octogenarian misconception reveals the true Corydoras arcuatus Elwin 1938 (Siluriformes: Callichthyidae) and a new Corydoras species from the Amazon basin

Abstract

After 80 years of misidentifications, the analysis of the holotype of Corydoras arcuatus plus several non‐type specimens attributed to this species allowed its recognition and also revealed a new species, both sharing the following diagnostic features: a long, arched, continuous black stripe that runs parallel to the dorsal profile of the body and extends at least from the anterior margin of the first dorsolateral body plate to the posterior portion of caudal peduncle; absence of transverse black bars on caudal fin; infraorbital 2 in contact with sphenotic and compound pterotic. In addition to these features, C. arcuatus can be distinguished from congeners by having the posterior margin of both dorsal and pectoral spines with laminar serrations directed towards their origins. The new species can be additionally distinguished from its congeners by presenting the following combination of features: ventral surface of trunk entirely or partially covered by relatively large and coalescent platelets; absence of spots or blotches on dorsal fin; and posterior margin of both dorsal and pectoral spines with serrations directed towards their tips. Finally, an identification key to all arc‐striped species of Corydoras is provided.

Corydoras fulleri (Siluriformes: Callichthyidae), a new catfish species from the rio Madeira basin, Peru

“…Convergent colour patterns have apparently played an important part in Corydoradinae evolution, as supported by several studies ( e.g ., Alexandrou et al ., 2011; Britto, 2003; Britto et al ., 2009; Lima & Sazima, 2017; Nijssen & Isbrücker, 1980a, 1980c; Tencatt et al ., 2013, 2019; Tencatt & Britto, 2016; Tencatt & Ohara, 2016a, 2016b; Tencatt & Pavanelli, 2015). While the data gathered by these papers makes it clear that snout shape is one of the most practical ways to differentiate the species with convergent colour patterns, their recognition goes far beyond that.…”

“…The Callichthyidae are armoured catfishes that can be promptly recognized among other Siluriformes by having two longitudinal series of dermal plates on their flanks (Reis, 1998, 2003). The family is currently comprised of more than 200 species which are grouped into eight genera, including Corydoras Lacépède, 1803, with 175 valid species, which makes it the most species‐rich genus of the family and also of Siluriformes (Lima & Britto, 2020; Tencatt et al ., 2019). Comprehensive studies attempting to understand the taxonomy and phylogenetic relationships of the species within Corydoras have been made ( e.g ., Alexandrou et al ., 2011; Britto, 2003; Eigenmann & Eigenmann, 1890; Ellis, 1913; Gosline, 1940; Nijssen, 1970; Nijssen & Isbrücker, 1967, 1980a, 1983a, 1986).…”