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.
Highlights
The Amazon river basin exhibits the greatest diversity of fish species in the world, harbouring more than 2,400 species (Reis et al 2016)
Members of Sarcoglanidinae are exclusively psammophilic, inhabiting loose patches of sand in both clearwater (Costa 1994; Zuanon and Sazima 2004) and blackwater streams. They are miniaturized catfishes that do not exceed 25 mm of standard length and are generally translucent, which allows for camouflage with the surrounding environment (Myers and Weitzman 1966; de Pinna 1989; Costa 1994)
Measurements are presented as percentages of standard length (SL), except for those related to head morphology, which are expressed as percentages of head length
Summary
The Amazon river basin exhibits the greatest diversity of fish species in the world, harbouring more than 2,400 species (Reis et al 2016). Despite being widespread and structurally simple, sand bottom habitats shelter a unique fish fauna that bears some remarkable morphological features: cryptic colour (usually translucent or light-coloured body), small body size, eyes dorsally placed (sometimes reduced or absent), and a specialized head morphology (Zuanon et al 2006) These characteristics can be found in several sand-dwelling (i.e. psammophilic) lineages of the family Trichomycteridae, such as the subfamily Sarcoglanidinae. Members of Sarcoglanidinae are exclusively psammophilic, inhabiting loose patches of sand in both clearwater (Costa 1994; Zuanon and Sazima 2004) and blackwater streams (de Pinna and Winemiller 2000; Costa et al 2019) They are miniaturized catfishes that do not exceed 25 mm of standard length (de Pinna 1989) and are generally translucent, which allows for camouflage with the surrounding environment (Myers and Weitzman 1966; de Pinna 1989; Costa 1994).
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