Cranial skeletogenesis and osteology of the redeye tetra Moenkhausia sanctaefilomenae

The skeletogenesis and osteology of the syncranium of the redeye tetra Moenkhausia sanctaefilomenae is described. Skeletal development is rapid, with many elements of the chondrocranium and splanchnocranium well formed prior to the onset of ossification. The chondrocranium develops from an initial set of cartilaginous precursors, and continued elaboration proceeds from a series of processes which expand and converge to form the floor of the cranial vault, the otic capsule, the supraorbital bridge and the ethmoid region. Prodigious growth is observed for a number of splanchnocranial elements, including the Meckel's cartilage and the ceratohyal cartilage. Ossification occurs in overlapping phases with initial ossification of the jaws and neurocranial floor followed by the splanchnocranium, the supraorbital bridges and the ethmoid and cranial vault. Teeth are observed primarily on the premaxilla and dentary, while a single tooth is present on the maxilla. Particular cartilages, which had originally formed in the early larva, appear to degenerate and have no ossified representative in the adult syncranium. The cranial development for M. sanctaefilomenae is compared to those of other characiforms.