Bowfin are often referred to as "living fossils", or "primitive fish" because they retained some of the primitive characters common to their ancestral predecessors, including a modified (rounded externally) heterocercal caudal fin, a highly vascularized gas bladder lung, vestiges of a spiral valve, and a bony gular plate. The bony gular plate is located underneath the head on the exterior of the lower jaw between the two sides of the lower jaw bone. Other distinguishing characteristics include long, sharp teeth, and two protruding tube-like nostrils. Unlike all of the most primitive actinopterygians, the scales of bowfin differ in that they are not ganoid scales, rather they are large, single-layered cycloid scales closer in similarity to more derived teleosts.