The development of the dentigerous bones and teeth in the hemiramphid fish Dermogenys pusillus (Atheriniformes, Teleostei).

ABSTRACT

The development of the dentition and dentigerous bones was studied in the hemiraphid Dermogenys pusillus using histological sections, scanning electron microscopy, and cleared and stained specimens. Five days after birth, the toothless tip of the lower jaw begins to grow longer than the tip of the upper jaw. The growth originates from small cartilaginous triangles connected with Meckel's cartilage. The peri- and enchondrial ossification of the growing cartilaginous bars advances rostrad. The pharyngeal tooth plates are formed by fusion of the slat-like dentigerous dermal bones with the bony fractions of the gill branches. Hence, the tooth plates are composite bones. The ventral tooth plate ist formed by the two ceratobranchials V and the basibranchial IV together with the respective dermal bones. The paired pharyngobranchials III and IV are fused with the dorsal tooth plate, and the pharyngobranchials II is fused with the two respective lateral tooth plates. Mineralization starts after birth in elements of the pharyngeal tooth plates and their teeth. There are no indications that the pedicel on which the tooth is established is formed by the enamel organ, which is covered by pulpal cells. The enamel organ originates from the stratum basale of the oropharyngeal epithelium and moves within the jaw from labial toward lingual, the site of the establishment of the tooth. The anlage of the tooth on the tooth plates of the pharynx lies at the level of the tooth base.