Cladistia

Cladistia is a small, early-diverging lineage of ray-finned fishes (Actinopterygii). In many classifications, it is treated as a distinct class containing the order Polypteriformes, whose living members are the bichirs (Polypterus) and the reedfish (Erpetoichthys calabaricus). Together they form the extant representatives of this lineage, found primarily in tropical Africa.

Anatomy and physiology of cladistians are marked by elongated bodies and heavy ganoid scales. They possess a series of dorsal finlets rather than a single, continuous dorsal fin, and they retain a relatively primitive skull and jaw structure compared with most other actinopterygians. Many species have lungs or lung-like air-breathing organs, enabling them to gulp air at the surface and survive in stagnant or seasonally dry waters.

Distribution and ecology: Bichirs and reedfish inhabit slow-moving rivers, swamps, and floodplains across sub-Saharan Africa. The reedfish (Erpetoichthys calabaricus) is notable for its ability to aestivate in mud during drought, forming a mucus cocoon that helps it survive long periods without water.

Reproduction and life history: Most species lay eggs (oviparous), and parental care is generally limited. Cladistians are among the most primitive surviving actinopterygians, making them valuable for understanding early ray-finned fish evolution. In some classifications, Polypteriformes are treated as the sole living order within Cladistia, underscoring its status as a basal lineage within Actinopterygii.

Human context: Bichirs are kept in aquariums and are appreciated for their distinctive appearance and resilience, though they require large tanks and appropriate water conditions.