Abstract
The genus Isistius Gill, 1865, which belongs to the family Dalatiidae, currently has three valid species: Isistius brasiliensis Quoy & Gaimard, 1824, I. plutodus Garrick & Springer, 1964 and I. labialis Meng, Zhu & Li, 1985. The most common species, I. brasiliensis, has a wide geographic distribution, and can be found in subtemperate and tropical seas; a comparative analysis of specimens from different localities has never been done. This project proposes to thoroughly study the morphological variation of this species along its distribution, elucidating if it is only one species or if it represents a complex of species. The other two species, I. plutodus and I. labialis, are known from only few specimens, raising doubts about their validity since I. brasiliensis is widely distributed. As I. labialis has only two collected specimens, one from the South China Sea and the other from the South Pacific Ocean, a detailed comparative analysis will be undertaken of these individuals to test the validity of this species. The same will be done with the five known specimens of I. plutodus, three from the South Pacific Ocean and two from the Western Atlantic Ocean. The representatives of the three species will be studied with the purpose of identifying them morphologically and re-describing them through more precise characters. Therefore, this study will analyze minutely the external morphology, such as coloration, dentition, dermal denticles, body proportions, and internal morphology, such as the skeleton, musculature, lateral line canals, of the known species, also covering morphometric and meristic aspects, to better define the genus and provide relevant morphological subsidies that may integrate future phylogenetic analysis of genera within the family. (AU)
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