Thayeria is a small genus of characins (family Characidae) from the freshwaters of Brazil, Colombia, Peru, and French Guiana. The atlas covers 3 species, ranging 1.5–3 in, sharing a distinctive silhouette: a deep, laterally compressed body carried at a head-up, tail-down angle in the water column rather than swimming level, with a bold dark stripe running diagonally from the caudal peduncle up into the lower lobe of the tail fin.
The genus is best known to hobbyists through the penguin tetra (Thayeria boehlkei), a long-standing staple of the community aquarium trade prized for that quirky nose-up posture and easy, peaceful schooling behaviour. The half-striped penguin tetra (T. ifati) and blackline penguinfish (T. obliqua) are less frequently seen but share the same general build and temperament. All 3 species in the atlas carry a Least Concern IUCN status, consistent with a genus that remains widespread across blackwater and clearwater habitats of the Amazon and Orinoco drainages.