Development of the musculus levator externus IV and the musculus obliquus posterior inHaplochromis elegans trewavas, 1933 (teleostei:Cichlidae): A discussion on the shift hypothesis

Abstract

An ontogenetic study of several postembryonic stages of Haplochromis elegans shows that the muscle referred to as “musculus levator externus IV” by previous authors in the adult stage of cichlid fishes is a compound muscle composed of the M. levator externus IV and the central portion of the M. obliquus posterior. Thus the supposed shift of the insertion area of the fourth external levator muscle from the fourth epibranchial to the fifth ceratobranchial, as deduced from adult morphology only, did not occur. Although this ontogenetic discovery does not change the functional specializations ascribed to the muscle by previous authors, it could have very important implications for the phylogenetic placement of the Cichlidae relative to such major taxa as Labroidei and Embiotocidae.