Morphological and histological data on the structure of the lingual toothplate of Arapaima gigas (Osteoglossidae; Teleostei)
The pirarucu, Arapaima gigas (Osteoglossidae) has a basibranchial toothplate that supports a great density of teeth and helps the food transfer from the oral cavity towards the oesophagus. The lingual teeth appear early during ontogeny of the hyoid and branchial skeleton. On the basibranchial toothplate the teeth are closely set but without any connection, contrary to the “coalesced teeth”. The lingual teeth are 4 mm long and 1.0 to 1.5 mm wide; they are constituted of a cone of orthodentine with a distal cap of enameloid. Dentine is divided into two layers: an inner layer of circumpulpal dentine and an external one of pallial dentine. A peculiar specificity of the lingual teeth is the presence of plicidentine in their basal part. So in Actinopterygii, plicidentine is not limited to lepisosteids only. Owing to (i) the different aspect of plicidentine in the two taxa and (ii) their relative phylogenetic distance, we can interprete plicidentine in Actinopterygii as a morphofunctional adaptation to a predation diet.