THE EMBRYONIC AND LARVAL DEVELOPMENT OF POLYPTERUS-SENEGALUS CUVIER, 1829 - ITS STAGING WITH REFERENCE TO EXTERNAL AND SKELETAL FEATURES, BEHAVIOR AND LOCOMOTORY HABITS

The embryonic and larval development of the Polypteriformes, the presu med sister group of all other living actinopterygians, is poorly known . The main reason is the scarcity of successful breedings in captivity and therefore the lack of developmental series of any one polypterid species. A series of five successful breedings of P. senegalus now mak es it possible to define developmental stages of this species based on numerous closely timed specimens. The staging given here focuses on e xternal embryonic and larval features: epidermal surface structures do cumented by SEM, colour pattern, development of fins and squamation, l arval feeding and locomotory behaviour. The development of P. senegalu s is characterized by a long free embryonic phase. Suction feeding is performed from the beginning of larval life (apterolarval phase). The pectoral fins start to become employed for slow locomotion and as supp ortive structures at around the same time. Olfactorily guided prey cap ture, however, is observed later in the pterolarval phase. Quantitativ e kinematic data also demonstrate a change in the mode of undulatory l ocomotion during this phase. Sustained axial undulation becomes confin ed to the posterior abdominal and caudal region of the body. At about the same time the paraxial high frequency undulation of the pectoral f in fold is replaced by the characteristic propeller-like movement of m uch greater amplitude and wavelength. Surfacing for aerial breathing i s not seen before a marked change in colouration has taken place at th e beginning of the juvenile period. The external gills slowly become r educed during this period. The definitions of larval and juvenile stag es given here may advance understanding of developmental processes in the ontogeny of these primitive actinopterygians, and may serve as a t ool for comparison with the ontogeny of Tetrapoda and Dipnoi, as well as to that of some ''primitive'' groups of Actinopterygii. Judging fro m its distribution among extant taxa, embryonic and larval ciliation i s a character that most probably belongs to the grundplan double dagge r of Osteognathostomata. Phylogenetic evaluation is not so clear for t he two other prominent embryonic and larval specializations found in P olypterus: upper labial attachment glands and opercular external gills . (C) 1997 The Royal Swedish Academy of Sciences. Published by Elsevie r Science Ltd.