New species of the miniature genus Gelanoglanis (Siluriformes: Auchenipteridae) from the Tocantins River basin (Brazil) and osteological description of G. nanonocticolus

Abstract

A new species of Gelanoglanis is described based on specimens collected in the Tocantins River, a tributary of the Amazon Basin. The new species is distinguished from congeners by unusual features to the genus such as the pelvic fin falling short of the urogenital opening by a distance larger than the anal-fin length, the first unbranched dorsal and pectoral-fin rays not ossified as spines, the dorsal-fin spinelet absent and the adipose fin in adults preceded by a long fleshy ridge. The new species is further distinguished from congeners by its soft, sinuous snout tip and morphometric proportions of the body and head. The new species shares most putative synapomorphies of the genus, as well as the miniaturized condition evidenced by a diminutive body size and reduced ossifications and lateral sensory system. An elongate dorsal process of the cleithrum is posited as an additional synapomorphy for the genus. An osteological description of Gelanoglanis nanonocticolus based on high-resolution X-ray computed tomography is also provided. http://zoobank.org/urn:lsid:zoobank.org:pub:BA3FE72D-FEF84-7A7-B751-2A15EA52C203.

Two new miniature translucent catfish species of the rare genus Tridens (Siluriformes: Trichomycteridae) from the Madeira River basin, northern Brazil

“…Furthermore, T. chicomendesi is so far only known from its type locality, increasing its vulnerability to any human‐related environmental disturbance. Considering the raising interest in the taxonomy and systematics of miniature siluriforms ( e.g ., Calegari et al ., 2014; Calegari & Reis, 2017; Carvalho et al ., 2016; Rocha et al ., 2012), and, more specifically, miniature trichomycterids ( e.g ., Henschel et al ., 2018; Henschel, Bragança et al ., 2020; Henschel, Lujan et al, 2020; de Pinna & Dagosta, 2022), even more advances in the knowledge of miniature species can be expected.…”

Quantifying shortfalls in the knowledge on Neotropical Auchenipteridae fishes

“…It is also necessary to highlight the importance of being cognizant of intrinsic features of the natural history of species to better understand what is contributing to the knowledge gaps. The Auchenipteridae family is known by its distinctive habit of using submerged trunks as diurnal shelters (in genera such as Balroglanis , Liosomadoras , Tatia and Trachelyichthys ; Birindelli & Zuanon, 2012) or by foraging at twilight and during the night on the surface of the water (such as the miniature species of Gelanoglanis ; Calegari & Reis, 2017). Because of these peculiarities, collecting fish from this family requires using diverse methods such as manual collecting inside trunks or ichthyoplankton nets.…”

“…According to Ota et al (2015), three factors may be responsible for the increase in description rates of siluriforms from 2001 onwards: Birindelli & Zuanon, 2012) or by foraging at twilight and during the night on the surface of the water (such as the miniature species of Gelanoglanis; Calegari & Reis, 2017). Because of these peculiarities, collecting fish from this family requires using diverse methods such as manual collecting inside trunks or ichthyoplankton nets.…”

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]).…”