Hemiodus is a genus of halftooths from South America with the greatest species richness in the Amazon Basin, but also found in the Orinoco, Essequibo, Paraná–Paraguay and Parnaíba River basins. Depending on the species involved, these elongate fish reach a length of .
Fossil remains are known from the Middle Miocene-aged Pebas Formation of Peru.
Species Hemiodus has the following species classified within it: Hemiodus amazonum (Humboldt, 1821) Hemiodus argenteus Pellegrin, 1909 Hemiodus atranalis (Fowler, 1940) Hemiodus bimaculatus Nogueira, Langeani & Netto‐Ferreira, 2019 Hemiodus goeldii Steindachner, 1908 Hemiodus gracilis Günther, 1864 Hemiodus huraulti (Géry, 1964) Hemiodus immaculatus Kner, 1858 Hemiodus iratapuru Langeani & C. L. R. Moreira, 2013 Hemiodus jatuarana Langeani, 2004 Hemiodus langeanii Beltrão & Zuanon, 2012 Hemiodus microlepis Kner, 1858 Hemiodus ocellatus (Vari, 1982) Hemiodus orthonops C. H. Eigenmann & C. H. Kennedy, 1903 Hemiodus parnaguae C. H. Eigenmann & Henn, 1916 Hemiodus quadrimaculatus Pellegrin, 1909 (Barred hemiodus) Hemiodus semitaeniatus Kner, 1858 (Halfline hemiodus) Hemiodus sterni (Géry, 1964) Hemiodus ternetzi G. S. Myers, 1927 Hemiodus thayeria J. E. Böhlke, 1955 Hemiodus tocantinensis Langeani, 1999 Hemiodus tucupi Silva, Nogueira, Netto-Ferreira, Akama & Dutra, 2020 Hemiodus unimaculatus (Bloch, 1794) Hemiodus vorderwinkleri (Géry, 1964)
References