Understanding morphological variability in a taxonomic context in Chilean diplomystids (Teleostei: Siluriformes), including the description of a new species

Abstract

Following study of the external morphology and its unmatched variability throughout ontogeny and a re-examination of selected morphological characters based on many specimens of diplomystids from Central and South Chile, we revised and emended previous specific diagnoses and consider Diplomystes chilensis, D. nahuelbutaensis, D. camposensis, and Olivaichthys viedmensis (Baker River) to be valid species. Another group, previously identified as Diplomystes sp., D. spec., D. aff. chilensis, and D. cf. chilensis inhabiting rivers between Rapel and Itata Basins is given a new specific name (Diplomystes incognitus) and is diagnosed. An identification key to the Chilean species, including the new species, is presented. All specific diagnoses are based on external morphological characters, such as aspects of the skin, neuromast lines, and main lateral line, and position of the anus and urogenital pore, as well as certain osteological characters to facilitate the identification of these species that previously was based on many internal characters. Diplomystids below 150 mm standard length (SL) share a similar external morphology and body proportions that make identification difficult; however, specimens over 150 mm SL can be diagnosed by the position of the urogenital pore and anus, and a combination of external and internal morphological characters. According to current knowledge, diplomystid species have an allopatric distribution with each species apparently endemic to particular basins in continental Chile and one species (O. viedmensis) known only from one river in the Chilean Patagonia, but distributed extensively in southern Argentina.

Otomorphs (= otocephalans or ostarioclupeomorphs) revisited

“…Major differences include: (1) a few molecular studies have questioned the monophyly and relationships of the Characiformes (Nakatani et al, 2011;Chen et al, 2013;Chakrabarty et al, 2017), but monophyly of the group and its position as the sister to Gymnotiformes + Siluriformes was recently supported by other molecular studies (Arcila et al, 2017;Betancur-R et al, 2017); (2) the family Diplomystidae appears as the most primitive catfish group in morphological studies of Siluriformes (e.g., Arratia, 1987;Grande, 1987), whereas Nematogenyidae plus other loricarioids is the sister to Diplomystidae plus all other catfishes in molecular studies (e.g., Sullivan et al, 2006;Arcila et al, 2017;Betancur-R et al, 2017). For other references on the subject see Arratia, Quezada-Romegialli (2017). Most extant ostariophysans are primarily freshwater fishes with a global distribution (except Antarctica, Greenland, and New Zealand), but there are about 120 marine species restricted to the Siluriformes (Nelson et al, 2016).…”

Phylogenetic classification of bony fishes

“…Morphological synapomorphies : see G Arratia [192], G Arratia [194], MCC de Pinna [195], MCC de Pinna [196], G Arratia and C Quezada-Romegialli [200].

Diplomystidae

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River science and management issues in Chile: Hydropower development and native fish communities

“…Overall, the fish fauna of this region of Chile is poorly researched. Baseline studies undertaken as part of the regulatory EIA recorded a fish species not described for Chile before; the primitive catfish Olivaichthys viedmensis (Arratia & Quezada‐Romegialli, ). The proposed hydropeaking operations in the Baker River were expected to have daily stage fluctuations >3 m, with water level changes of 10 cm min −1 over a 30 min cycle in a section of river network important for the reproduction of O. viedmensis .…”