Osteology of Dwarfgobies Eviota and Sueviota (Gobiidae: Gobiomorpharia), With Phylogenetic Inferences Within Coral Gobies

Abstract

Eviota and Sueviota are two genera of cryptobenthic fishes of the family Gobiidae commonly known as dwarfgobies, that collectively contain 142 species. Despite thorough descriptions of the variation of their external morphology, little is known about variations on their skeleton. Combining traditional clearing-and-staining technique with computed scanning microtomography, we examined five species of Sueviota and 40 species of Eviota, representing the two major monophyletic groups in the latter genus, the “branched clade” and “unbranched clade,” named for their pectoral ray morphology. The purpose of this study was to provide generalized descriptions for both genera and highlight potentially phylogenetically informative characters that will aid in future classification of this diverse assemblage of fishes. The posterior portion of the mesethmoid was found to be unossified in eight species of Eviota from the unbranched clade. Twenty-five vertebrae (vs. 26 vertebrae) are present only in species of the unbranched clade of Eviota, and it is considered another potential synapomorphy for this clade. Direct contact between the retroarticular and the anterior edge of the interopercle without the retroarticular-interopercle ligament occurs in all species of Eviota and Sueviota, being interpreted as a potential synapomorphy grouping these two genera. The posterior edge of the interopercle is notched in all species of Eviota and Sueviota, as well as in the closely related genera Bryaninops, Pleurosicya, and Paragobiodon. In species of Sueviota and the branched clade of Eviota, the notch is deep, and there is an additional posteroventral process, forming a wrench-like posterior edge of the interopercle. This wrench-shaped interopercle is a potential synapomorphy, grouping Sueviota with representatives of the branched clade of Eviota. Individual and ontogenetic variations are discussed, including an assessment of the characters previously proposed for characterizing the branched and unbranched clades of Eviota.