Saturday, March 25, 2017

[Ichthyology • 2017] Understanding Morphological Variability in A Taxonomic Context in Chilean Diplomystids (Teleostei: Siluriformes), Including the Description of A New Species, Diplomystes incognitus


Diplomystes incognitus Arratia & Quezada-Romegialli, 2017

Figure 18: Diplomystes incognitus sp. nov. in a recreation of its natural environment.
Young individual, ca. 93 mm SL, from Ñuble River at Nahueltoro Bridge, Itata Basin.

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.


Figure 18: Diplomystes incognitus sp. nov. in a recreation of its natural environment.
 Young individual, ca. 93 mm SL, from Ñuble River at Nahueltoro Bridge, Itata Basin.  
 


Diagnosis. Diplomystid that is distinguished from all congeners by the possession of the skin of head, body, and fins densely covered by round, short papillae giving the skin a blackberry-like or verrucose aspect in large individuals; with a short head, slightly squarish and as long as broad (versus slightly longer more triangular-shaped head); high dorsal fin, ca. 20% of SL (range 17–25%) and triangularly-shaped (versus slightly rhomboidal); maxilla with 7–9 teeth (vs. 8–13 in D. chilensis, 11–13 in D. nahuelbutaensis, and 12–19 in D. camposensis); with 10 infraorbital bones, as in D. nahuelbutaensis, but the dorsalmost compound bone is absent; urogenital pore and anus placed between posterior tips of pelvic fins as in D. chilensis (vs. urogenital pore and anus placed between pelvic fins or in between the distal tips of pelvics and anal fin); and absence of pores of axillary gland with occasionally four on one side of body (vs. two or three pores).

Etymology. The specific name incognitus is in reference that recognition of the species was obscured by the assumption that Diplomystes chilensis also extended south of Maipo Basin.

Geographical distribution. In Rapel, Mataquito, Maule, and Itata Basins.


 Gloria Arratia​​ and Claudio Quezada-Romegialli​. 2017.  Understanding Morphological Variability in A Taxonomic Context in Chilean Diplomystids (Teleostei: Siluriformes), Including the Description of A New Species.  PeerJ 5:e2991.  DOI: 10.7717/peerj.2991


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