Distribution:
Africa.
Habitat:
Freshwater in floodplains and estuaries.
Remarks:
The scientific name Polypteridae comes from the Greek poly, meaning "many" and pteron, meaning "wing", which refers to the Bichirs' unique fins. These fishes are also known as "Flagfins" because of the dorsal fin, which is actually composed of 5-18 smaller fins or finlets. Each finlet has a single spine with soft rays that originate from the spine. This setup is very different than that of all other bony fishes, in which the dorsal rays emerge from the body of the fish. Bichirs have long, eel-like bodies covered with thick rhombic ganoid scales (bone-like scales sheathed in ganoin) and in addition, have lobe-like pectoral fins similar in appearance to those of the lobe-finned fishes of the class Sarcopterygii.
Bichirs inhabit the low-oxygen, swamp-like floodplains of Africa, and of particular interest is their respiratory system. Juvenile Bichirs have branched external gills which disappear as the fish ages. During adulthood, the fish have fully-functional internal gills, but in addition the swim bladder also serves as a respiratory organ. The swim bladder has two lobes, one more developed than the other, and attaches to the esophagus. In addition to using their gills, Bichirs can breath by gulping air into this lung-like swim bladder.
Members of this family have many primative characteristics unknown in other extant bony fishes, and many derived traits that are unique to the taxon. There is much debate over where to classify the family, as it is unclear whether they should be placed in the class Actinopterygii, Sarcopterygii, or in their own class, Brachiopterygii.
Bichirs have traits that are somewhat sarcopterygian (shared by certain lobe-finned fishes: lobelike fins, two gular plates, feathery external gills) as well as traits that are somewhat actinopterygian (shared by certain primitive ray-finned fishes: spiracles, ganoid scales). However, classification is extremely difficult because while these characteristics seem similar to those of other taxa, the internal construction is very different than that of any known fish. For example, while the pectoral fins of the Bichirs are lobe-shaped, they are much more elaborate than those of the lobe-finned fishes, to the point where they are described as being "overelaborate."
For simplification, we use the taxonomic hierarchy of Nelson (2006), and place this family under Actinopterygii : Polypteriformes : Polypteridae. This family comprises 2 genera (Erpetoichthys and Polypterus), and about 16 species.
References:
Helfman et al. 1997,
Nelson 2006