Osteology and myology of the cephalic region and pectoral girdle of Cetopsis coecutiens Spix & Agassiz, 1829, comparison with other cetopsids, and comments on the synapomorphies and phylogenetic position of the Cetopsidae (Teleostei : Siluriformes)

The cephalic and pectoral girdle structures of the cetopsid Celopsis coecutiens (Cetopsinae) are described and compared with those of another species of the subfamily Cetopsinae, Hemicetopsis candiru, and of one species of the single genus of the subfamily Helogeninae, Helogenes marmoratus, as well as of several other catfishes. Our observations and comparisons support Me's 1991 and de Pinna's 1998 phylogenetic hypothesis, according to which the cetopsids occupy a rather basal position within the Siluriformes. In addition, our observations and comparisons pointed out three new, additional characters to diagnose the family Cetopsidae, namely : 1) presence of a muscle 6 of the mandibular barbels; 2) medial branchiostegal rays long and Stout; 3) mandibular barbels originate on the posteroventral Surface of their irregularly shaped basal cartilages.