Osteology and myology of the cephalic region and pectoral girdle of Pimelodus blochii , comparison with other pimelodines, and comments on the synapomorphies and phylogenetic relationships of the Pimelodinae (Ostariophysi: Siluriformes)

Abstract

The cephalic and pectoral girdle structures of the pimelodin Pimelodus blochii (Pimelodus group) are described and compared to those of representatives of the two other main pimelodin groups, namely Calophysus macropterus (Calophysus group) and Pseudoplatystoma fasciatum (Sorubim group), and of a representative of the peculiar pimelodin genus Hypophthalmus, H. edentatus, and several other catfishes, as the foundation for a discussion on the synapomorphies and phylogenetic relationships of the Pimelodinae. Three new, additional potential synapomorphies to support the monophyly of the Pimelodinae are pointed out: (1) presence of a 'muscle 1 of the mandibular barbels' running from the antero-ventro-mesial surface of the cartilaginous plates carrying these barbels to the dentaries; (2) presence of a muscle tensor tripodis running from the posterior surface of the neurocranium to the dorsal surface of the swimbladder near the tripus; and (3) presence of a 'drumming muscle of the swimbladder' running from the parapophyses of the fourth vertebra and, eventually, the posterior surface of the neurocranium, to the antero and antero-ventral surface of the swimbladder. The subfamilies Pimelodinae, Heptapterinae and Pseudopimelodinae seem to constitute a monophyletic assemblage, thus contradicting the commonly accepted idea that the family Pimelodidae is a polyphyletic clade.