Zoology 115 (2012) 84–116 Contents lists available at SciVerse ScienceDirect Zoology jou rnal h om epa g e: www . elsevier.de/zool Anatomy and evolution of the mandibular, hyopalatine, and opercular muscles in characiform fishes (Teleostei: Ostariophysi) Aléssio Datovo ∗ , Ricardo M.C. Castro Laboratório de Ictiologia de Ribeirão Preto, FFCLRP, Departamento de Biologia, Universidade de São Paulo, Av. dos Bandeirantes, 3900, 14040-901 Ribeirão Preto, SP, Brazil a r t i c l e i n f o Article history: Received 2 April 2011 Received in revised form 10 August 2011 Accepted 11 September 2011 Keywords: Adductor mandibulae Characiformes Fish musculature Myology a b s t r a c t The Characiformes are distributed throughout large portions of the freshwaters of Africa and America. About 90% of the almost 2000 characiform species inhabit the American rivers, with their greatest diver- sity occurring in the Neotropical region. As in most other groups of fishes, the current knowledge about characiform myology is extremely poor. This study presents the results of a survey of the mandibular, hyopalatine, and opercular musculature of 65 species representing all the 18 traditionally recognized characiform families, including the 14 subfamilies and several genera incertae sedis of the Characidae, the most speciose family of the order. The morphological variation of these muscles across the order is documented in detail and the homologies of the characiform adductor mandibulae divisions are clarified. Accordingly, the mistaken nomenclature previously applied to these divisions in some characiform taxa is herein corrected. Contradicting some previous studies, we found that none of the examined characiforms lacks an A3 section of the adductor mandibulae, but instead some taxa have an A3 continuous with A2. Derived myological features are identified as new putative synapomorphies for: the Characoidei; the clade composed of the Alestidae, Characidae, Gasteropelecidae, Cynodontoidea, and Erythrinoidea; the clade Cynodontoidea plus Erythrinoidea; the clade formed by Ctenoluciidae and Erythrinidae; the Serrasalmi- nae; and the Triportheinae. Additionally, new myological data seems to indicate that the Agoniatinae might be more closely related to cynodontoids and erythrinoids than to other characids. © 2012 Elsevier GmbH. All rights reserved. 1. Introduction The Characiformes are a large group of freshwater fishes that currently circumscribe 1967 valid species (Eschmeyer and Fong, 2011) and a large number of still undescribed taxa (Vari, 1998; Reis et al., 2003). The characiforms are distributed throughout the continental waters of large portions of the Americas and Africa. The order’s greatest diversity is found in the Neotropics, where these fishes are of outstanding ecological and economic impor- tance (Nelson, 2006), inhabiting all the major hydrographic basins of this region, from the southern boundaries of the United States of America to central Chile and Argentina (Zanata and Vari, 2005). The Characiformes exhibit a remarkable variety of forms, body sizes – ranging from 13 to 1400 mm of standard length –, and feeding habits, with predator, herbivore, detritivore, and lepidophagous species (Géry, 1977; Goulding, 1980; Sazima, 1983; Goulding et al., 1988; Reis et al., 2003; Nelson, 2006). ∗ Corresponding author. Present address: Museu de Zoologia da Universidade de São Paulo (MZUSP), Laboratório de Ictiologia. Av. Nazaré, 481, 04263-000 São Paulo, SP, Brazil. E-mail address: adatovo@gmail.com (A. Datovo). According to Buckup (1998), Reis et al. (2003), and Nelson (2006), the order Characiformes is composed of 18 fam- ilies: Acestrorhynchidae, Alestidae, Anostomidae, Characidae, Citharinidae, Chilodontidae, Crenuchidae, Ctenoluciidae, Curimati- dae, Cynodontidae, Distichodontidae, Erythrinidae, Gasteropeleci- dae, Hemiodontidae, Hepsetidae, Lebiasinidae, Parodontidae, and Prochilodontidae. Among these families, that of the Characidae sensu Buckup et al. (2007) is the most speciose, encompassing approximately 61% of the order’s diversity, according to Eschmeyer and Fong (2011). The current knowledge about the muscular system of the Characiformes is scant. Most contributions to the field are derived from a limited number of structures investigated, usually in restricted subgroups of characiforms (e.g., Alexander, 1964; Vari, 1979, 1983; Lauder, 1981; Machado-Allison, 1982, 1983, 1985; Weitzman and Fink, 1985; Gosline, 1989; Vari, 1995; Buckup, 1998; Weitzman and Malabarba, 1999; Castro and Vari, 2004; Mirande, 2009, 2010). To date, only Howes (1976) has published a major arti- cle dedicated to the comparative study of skeletal musculature of some groups of highly derived predatory characiforms. In the present study, a broad survey of the mandibular, hyopalatine, and opercular muscles across the Characiformes is accomplished. The morphological variation of the cranial muscles of representatives of all families of the order is described and the 0944-2006/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. doi:10.1016/j.zool.2011.09.008