A new species of Hoplomyzon (Siluriformes: Aspredinidae) from Maracaibo Basin, Venezuela: osteological description using high-resolution computed microtomography of a miniature species

Abstract

A new miniature species of banjo catfish of the genus Hoplomyzon is described from the Lake Maracaibo Basin in Venezuela. The new species is distinguished from all its congeners by the straight anterior margin of the mesethmoid (vs. a medial notch); a smooth and straight ventral surface of the premaxilla (vs. presence of bony knobs on the ventral surface of premaxilla); absence of teeth on dentary (vs. teeth present on dentary); configuration of ventral vertebral processes anterior to anal fin, which are composed of single processes anterior to anal-fin pterygiophore (vs. paired process); presence of several filamentous barbel-like structures on the ventral surface of head of adults (vs. small papillous structures in the ventral surface of head of adults); and 8 anal-fin rays (vs. 6 or 7). An extensive osteological description is made of the holotype using high-resolution x-ray computed microtomography (HRXCT).Keywords: Endemism, Ernstichthys intonsus, Miniaturization, Synapomorphy, Taxonomy.Se describe una nueva especie miniatura de pez banjo perteneciente al género Hoplomyzon, proveniente de tributarios del Lago Maracaibo en Venezuela. La nueva especie se diferencia de sus congéneres por presentar el margen anterior del mesetmoide recto (vs. con una hendidura central); superficie ventral de la premaxila lisa y recta (vs. superficie ventral de la premaxila con protuberancias óseas); ausencia de dientes en el dentario (vs. dientes presentes); configuración de los procesos anteriores ventrales de la aleta anal, los que están compuestos de procesos simples anteriores al pterigióforo de la aleta anal (vs. procesos dobles); presencia de varias estructuras en forma de barbillas en la superficie ventral de la cabeza (vs. pequeñas estructuras en forma de papilas en la superficie ventral de la cabeza); y 8 radios en la aleta anal (vs. 6 o 7). Una extensiva descripción osteológica del holotipo fue realizada utilizando microtomografía computarizada de rayos X de alta resolución (HRCXCT).

Two new catfish species of typically Amazonian lineages in the Upper Rio Paraguay (Aspredinidae: Hoplomyzontinae and Trichomycteridae: Vandelliinae), with a biogeographic discussion

“…However, details of the shape of the plates differ in E. taquari and Hoplomyzon species. In Hoplomyzon, the shields are roundish and symmetrical in shape (Carvalho et al, 2017). In E. taquari, contrastingly, the respective plates are roughly triangular and slanted posteriorly.…”

“…For example, the species lacks premaxillary and dentary teeth, like Dupouyichthys, Micromyzon, and other Ernstichthys. The significance of this trait, however, is not as decisive as it once was, because Hoplomyzon cardosoi also lacks teeth on both bones (Carvalho et al, 2017).…”

“…Despite being such an obvious object of interest for morphological investigation, the anatomy of Hoplomyzontinae remained poorly-known until recently, with fragmentary information scattered in various publications. This situation began to change with Carvalho et al (2016) and Carvalho et al (2017) which offered an unprecedented picture of the osteology of Micromyzon orinoco and Hoplomyzon cardosoi. Hoplomyzontine taxonomy is relatively tidy, as might be expected for such a small group, but some generic limits are based on rather limited character evidence.…”

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]).…”