A new psammophilic species of the catfish genus Ammoglanis (Siluriformes, Trichomycteridae) from the Amazon River basin, northern Brazil

Abstract

Ammoglanis obliquussp. nov., a minute catfish species reaching a maximum adult size of 15.5 mm, is described from the Rio Preto da Eva drainage in the central Brazilian Amazon. It is distinguished from all of its congeners in possessing an exclusive combination of character states, including the presence and number of premaxillary and dentary teeth, number of interopercular and opercular odontodes, presence of cranial fontanel, number of dorsal-fin rays, number of anal-fin rays, number of caudal-fin rays, number of pelvic-fin rays, number of pectoral-fin rays, absence of pelvic splint, antorbital morphology, and absence of supraorbital and autopalatine morphology. It is considered to be a member of a clade also including A. pulex and A. amapaensis due to the unique oral, antorbital, and autopalatine morphology. Ammoglanis obliquus is regarded as more closely related to A. pulex than to any other congener, as both species exhibit a similar colour pattern, an absence of the metapterygoid, and the presence of two finger-like projections on the chin region.

Ammoglanis natgeorum, a new miniature pencil catfish (Siluriformes: Trichomycteridae) from the lower Atabapo River, Amazonas, Venezuela

“…Previously, A. pulex and A. amapaensis were considered to be more closely related to each other than to congeners due to their shared, distinctive antorbital, and autopalatine morphologies (Costa et al, 2019;Mattos et al, 2008). Henschel et al (2020) discussed the similarities between A. obliquus, A. pulex and A. amapaensis, and argued for a close relationship between these species, based on their shared subterminal mouth, scythe-shaped antorbital and a compact autopalatine with the lateral margin slightly concave and the medial margin slightly convex, having a small posterolateral process (de Pinna & Winemiller, 2000;Henschel et al, 2020;Mattos et al, 2008). Because A. natgeorum shares the same character states with these three species, it is hypothesized that A. amapaensis is sister to a putative clade composed of A. pulex, A. obliquus and A. natgeorum.…”

“…All species of Ammoglanis share a similar quadrate morphology, with its depth ranging 15–30% of its length (Costa, 1994; Costa et al ., 2019; de Pinna & Winemiller, 2000; Henschel et al ., 2020; Mattos et al ., 2008). Among the character states originally proposed by Costa (1994) to diagnose the genus, quadrate shape is the only character that has been confirmed throughout the genus, supporting the assignment of A. natgeorum to this genus.…”

“…A. natgeorum is distinguished from all congeners by having four to six premaxillary teeth and distinct pigmentation around the anal‐fin base. A similar dorso‐lateral coloration pattern is also present in A. pulex and A. obliquus (de Pinna & Winemiller, 2000; Henschel et al ., 2020). These two species and A. natgeorum share an overall similar and highly distinct live pigmentation pattern: presence of poorly defined bands of chromatophores visible in dorsal view and dark chromatophores in the interior of the body forming a banded pattern along the flank, which was considered by de Pinna and Winemiller (2000) to be exclusive among trichomycterids.…”

“…For example, the recent description of A. multidentatus from northeastern Brazil extended the geographical range of the genus 1000 km eastward (Costa et al ., 2019) and demonstrated for the first time that Ammoglanis occurs outside the Amazon/Orinoco megabasins. Whereas A. obliquus recently became the fourth species described from within the Amazon basin, suggesting that local populations within large drainage basins may represent new species, many undescribed species are likely yet to be discovered (Henschel et al ., 2020). This paper describes a new and clearly morphologically distinct species of Ammoglanis from a marginal habitat in the mouth of the Atabapo River (Figure 1), less than 150 km from the type locality of A. pulex , the only other species currently recognized from the Orinoco River basin.…”

Osteology of Tucanoichthys tucano Géry and Römer, an enigmatic miniature fish from the Amazon basin, Brazil (Teleostei: Characiformes: Characidae)

“…Miniaturization, the evolution of extremely small adult body size, is a common phenomenon among freshwater fishes, especially in the Neotropics from where over 200 miniature species (≤26 mm in standard length [SL] sensu Weitzman and Vari 1988) are already known (Toledo-Piza et al 2014) and new species continue to be discovered annually (e.g., Henschel 2016;Mendonça et al 2016;Carvalho et al 2016Carvalho et al , 2017Calegari and Reis 2017;Pastana et al 2017;Valdesalici and Nielsen 2017;Caires and Toledo-Piza 2018;Camelier et al 2018;Jerep et al 2018;Abrahão et al 2019;Costa et al 2019;Ohara et al 2019;Henschel et al 2020aHenschel et al , 2020bMattox et al 2020Mattox et al , 2021Lima et al 2021;Vieira and Netto-Ferreira 2021). Miniaturization is frequently associated with one of two evolutionary processes: (1) a simple evolutionary decrease in body size resulting in miniature versions of larger close relatives (the so-called proportional dwarves of Gould [1971]); and (2) shifts in the relative timing of gonadal development in relation to somatic development (progenesis) resulting in species with developmentally truncated adults that resemble the larval stages of closely related taxa (so-called developmentally truncated miniatures of Rüber et al [2007]; ; Britz et al [2014]).…”