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The family Muraenidae is one of the largest and most recognizable eel groups. Moray eels are key components of marine ecosystems but their relationships remain poorly understood. The phylogenetic relationships of the morays are examined herein using mitochondrial 12S and 16S sequence data, totaling 1673 bp for 139 taxa. The results of our analyses found support for a monophyletic family Muraenidae that is part of a monophyletic suborder Muraenoidei, which is revised to include the anguilliform families Heterenchelyidae and Myrocongridae, and to exclude the family Chlopsidae. The muraenids form two monophyletic subfamilies, Muraeninae and Uropterygiinae. Of the genera that had multiple species included for analysis, only the type genus of the family, Muraena, is found to be monophyletic. In the subfamily Uropterygiinae, Uropterygius is not recovered as a monophyletic genus. In the subfamily Muraeninae, the species-rich piscivorous genera, Enchelycore and Gymnothorax, and the durophagous genus, Echidna, are demonstrably not monophyletic. The monotypic Gymnomuraena is the sister group to all other muraenine species. The relationships within Muraenidae require much additional study and its genera remain in urgent need of revision. The order Anguilliformes is revised herein to include four suborders: Anguilloidei, Congroidei, Muraenoidei, and Synaphobranchoidei. All four families of the order Saccopharyngiformes are nested within Anguilliformes, recovered as part of a clade that includes Anguillidae; the saccopharyngiform families are referred to the suborder Anguilloidei sensu novum.

A new genus and species of Late Cretaceous euteleost, Avitosmerus canadensis, is described from an assemblage of fossil fishes found in a Late Cretaceous (Turonian) unnamed member (unit E) of the Great Bear Basin from Lac des Bois, Northwest Territories, Canada. It is a small fusiform fish characterized by a long slender supraorbital, the presence of a small suprapreopercle, branches of the preopercular sensory canal that reach the edge of the preopercle, and an anterior supraneural that is twice as large as those posterior to it. Additionally, elements of its caudal fin show a high degree of fusion. Avitosmerus is one of ten described Cretaceous basal euteleosts that are found worldwide (Avitosmerus, Barcarenichthys, Erichalcis, Gaudryella, Gharbouria, Humbertia, Kermichthys, Manchurichthys, Paravinciguerria, and Stompooria). Avitosmerus and Erichalcis are the only two basal euteleosts that have been described from the Cretaceous of North America. Placement of Avitosmerus into the Euteleostei is based on the presence of a free stegural, and the large first supraneural. Both of these characters are somewhat controversial and are in need of reexamination. Avitosmerus shares a number of characters with the other Cretaceous basal euteleosts, as well as Recent basal euteleosts, including a separate rostrodermethmoid and mesethmoid (Gaudryella, Erichalcis, Gharbouria, the Osmeridae, and the Coregonidae), lobate condyles of the hyomandibula (Avitosmerus, Gaudryella, and Gharbouria), leaf-shaped neural spine on the first preural centrum (Kermichthys), and the fusion of the parhypural, first, and second hypurals (Gaudryella).

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The Muhi quarry of Zimapán Hidalgo, Central México, is one of the most important Cretaceous fish localities of the country because of the great diversity of fishes, and the significance of their record in America. Here we present some advances of the stratigraphy, including a litostratigraphic description, a generalized report of the marine fauna recovered, and the depositional environment of the outcrop. The sequence consists of a light gray mudstone/biomicrite, with chert forming nodules and/or thin layers, and additional marls are intercalated; the strata are assigned to La Negra Facies of the Mid-Cretaceous (Albian-Cenomanian) El Doctor Formation from northeastern Querétaro, south-central and northwestern Hidalgo (this report). The lithology and fossils are indicative of open sea shelf to deep shelf margin Standard Facies Zones, comparable to the Standard Microfacies Types SMF 2 (microbioclastic limestone) and SMF 3 (pelagic mudstone).