Cephalic and Pectoral Girdle Muscles of the Clupeiform Denticeps

Animal Biology 58 (2008) 41–66 www.brill.nl/ab

Cephalic and pectoral girdle muscles of the clupeiform Denticeps clupeoides, with comments on the homologies and plesiomorphic states of these muscles within the Otocephala (Teleostei)

Rui Diogo* and Ignacio Doadrio

Museo Nacional de Ciencias Naturales, Madrid, Spain Laboratory of Functional and Evolutionary Morphology, Liège University, Belgium

Abstract The muscles of the cephalic region and pectoral girdle of Denticeps clupeoides are described and compared with those of other otocephalans (= clupeomorphs + ostariophysans). In general, the configuration of the cephalic and pectoral girdle muscles of Denticeps seems to correspond to the plesiomorphic condition for extant otocephalans, the main exceptions being: the dilatator operculi, which is rather small and is to a great extent covered in lateral view by the preopercle; the arrector dorsalis, which is not divided into two well-differentiated, separate sections; the protractor pectoralis, which is missing. Comments on the homologies, plesiomorphic states and evolution of the cephalic and pectoral muscles within the Otocephala are given.

Keywords Anatomy; Clupeiformes; Denticeps; evolution; myology; muscles; Ostariophysi; Otocephala; Teleostei

Introduction The Otocephala (Ostariophysi + Clupeomorpha) is one of the most diverse vertebrate groups (e.g., Lecointre, 1995; Zaragüeta-Balis et al., 2002; Nelson, 2006). The Ostario- physi comprise the Otophysi and Anatophysi (fig. 1) and includes more than 25% of teleostean species and about 68% of all freshwater fishes (Nelson, 2006). The otophysan clade includes the Siluriformes, Cypriniformes, Characiformes and Gymnotiformes, formally grouped by Sagemehl (1885) based to the presence of a complex chain of ossicles connecting the swimbladder to the inner ear – the Weberian apparatus. Anatophysi

*) Corresponding address: Rui Diogo, Department of Anthropology, The George Washington University, 2110 G St. NW, Washington, DC 20052, USA; e-mail: [email protected]

DENTICEPS DENTICIPITOIDEI ETHMALOSA CLUPEOIDEA ILISHA PRISTIGASTEROIDEA CLUPEOIDEI CLUPEIFORMES ENGRAULIS ENGRAULOIDEA THRYSSA CHANOS GONORYNCHUS PHRACTOLAEMUS GRASSEICHTHYS GONORYNCHIFORMES CROMERIA PARAKNERIA KNERIA ANATOPHYSI OTOCEPHALA CATOSTOMUS COBITIS OPSARIICHTHYS CYPRINIFORMES DANIO OSTARIOPHYSI BARBUS XENOCHARAX DISTICHODUS CHARACIFORMES CITHARINUS BRYCON BRACHYHYPOPOMUS STERNOPYGUS GYMNOTIFORMES OTOPHYSI GYMNOTUS DIPLOMYSTES CALLICHTHYS NEMATOGENYS TRICHOMYCTERUS SILURIFORMES CETOPSIS SILURUS CHRYSICHTHYS BAGRUS PIMELODUS

Figure 1. Phylogenetic relationships among extant otocephalans, modified from Diogo (in press) (for more details, see text). includes the Gonorynchiformes, considered the sister-group of otophysans following Greenwood et al. (1966) and Rosen and Greenwood (1970). In contrast to Ostariophysi, extant members of the superorder Clupeomorpha are mainly marine. The superorder contains some basal groups exclusively represented by fossil taxa, e.g. the Ellimmichthyiformes, and the Clupeiformes (herrings, anchovies and relatives). This latter order thus includes all extant clupeomorph species. The clupeiforms are among the most economically important fish species: heavily exploited by man for food, the immensity of their numbers also makes them an important food item for larger food fishes, as well as for a host of other marine life (e.g. Nelson, 2006). The order Clu peiformes comprises the Clupeoidei and the Denticipitoidei (fig 1). Within Clupeoidei, three major groups are recognized: Clupeoidea, Engrauloidea and Pristigasteroidea (fig. 1). Within the Denticipitoidei, one single species is recognized, Denticeps clupeoides Clausen 1959 (see Grande, 1985; Gourène and Teugels, 1994; Di Dario, 2002, 2004). Denticeps is thus the sister-group of all other extant clupeiforms, being, therefore, the most basal extant member of the order Clupeiformes (see fig.1 ) and, consequently, of the superorder Clupeomorpha (Grande, 1985; Di Dario, 2002, 2004). There is growing evidence to support the close relationship between the ostariophy- san and clupeomorph fishes (e.g., Lecointre, 1995; Zaragüeta-Balis et al., 2002; Saitoh et al., 2003; Inoue et al., 2004; Peng et al., 2006; Diogo, in press). Therefore, many authors have stressed the importance of taking into account the clupeomorphs, and