Senegal bichir

Polypterus senegalus is a basal ray-finned fish (order Polypteriformes) native to freshwater habitats across tropical Africa, including the Nile, Niger, Senegal, and Chad basins. Adults reach 30–40 cm in length and possess a distinctive elongated, cylindrical body covered in thick, diamond-shaped ganoid scales composed of ganoine and bone—a primitive feature shared with fossil actinopterygians. The dorsal fin is uniquely divided into 7–11 separate finlets, each with a spine and soft rays, giving the genus its name ("many fins"). Pectoral fins are fleshy and lobed, supported by an internal skeletal element, allowing limited terrestrial locomotion. Crucially, P. senegalus possesses paired ventral lungs (modified swim bladders) that function as air-breathing organs, enabling survival in hypoxic or drying water bodies. They are facultative air breathers that will drown if denied access to the surface. The species is nocturnal and carnivorous, feeding on insects, worms, crustaceans, and small fish. Reproduction involves external fertilization during the rainy season, with males using their cupped anal fin to receive and fertilize eggs. P. senegalus is widely used in evolutionary and developmental biology research as a living representative of the most basal extant ray-finned fish lineage, providing insights into the fin-to-limb transition and the evolution of terrestrial locomotion.