lateral line scales that reflect green in some lights, similar to Iguanodectes spilurus (the "green line lizard tetra"); P. dentatus' deeper pectoral keel and fin shape make the two relatively easy to differentiate. In other cases, different markings are present; Piabucus melanostoma can be told apart from other members of the genus by markings on its lower jaw, which is where its specific epithet comes from; "melano-" means "black" and "-stoma" means "mouth". P. caudomaculatus' specific epithet also originates from its appearance, because "caudo-" means "tail" and "maculatus" means "spotted", referring to the dark patch on the caudal peduncle. P. dentatus' markings have earned unidentified Piabucus tetras the nickname "chin tetra" amongst aquarium hobbyists. The dentition of Piabucus is relatively complete amongst characiform fishes, as is the case with the entire family Iguanodectidae (hence the name; "Iguanodectes" means "lizard bite"). The mouth is small and terminal, and the teeth contract at the base and flare out towards the tip. The maxilla is equipped with a full set of multicuspid incisors, and the premaxilla has one or two teeth on each side in all species, forming an "outer set". The exception to this is Piabucus melanostoma, which lacks this outer set. Taxonomy Piabucus is the least speciose genus in the family Iguanodectidae, with only 3 species. (Iguanodectes has 8, and Bryconops has 21.) These species are: Piabucus caudomaculatus (Vari, 1977) Piabucus dentatus (Kölreuter, 1763) Piabucus melanostoma (Holmberg, 1891) When originally classified, Piabucus was considered a characin (member of Characidae). In 1929, ichthyologist Carl H. Eigenmann moved it to the subfamily Iguanodectinae alongside the genus Iguanodectes, still in Characidae. James Erwin Böhlke reconfirmed this move through use of morphology in 1954. In 2011, research by Oliviera et al. showed that Bryconops was closely related to Iguanodectinae, and posited that the two clades be moved to the new family Iguanodectidae. Piabucus was first described in 1817 by German biologist Lorenz Oken when he named the species Piabucus dentatus. The true first member of the genus was not given a binomial name when described by Joseph Gottlieb Kölreuter in 1760, though he did introduce a genus Piabucu, and this was based on the work of Georg Marcgrave in his book Historia Naturalis Brasiliae from 1648. Many sources mistakenly report the baisonym of Piabucus dentatus as being Trutta dentata, partially because James Erwin Böhlke reported it as such in a 1954 paper. Subsequently, French ichthyologist