Investigators have also found that adult "T. penetrans" have different morphologies with respect to the shape of their head. Some have a rounded head, others have head shapes that resemble ski ramps more than anything else; still, others demonstrate head shapes that are very linear with a slight bulge at the nose. These morphologies were seen to be host-specific, as only fleas of some head-types were found in specific hosts. This, along with genetic differences among the "T. penetrans" fleas that infect different host animals, may suggest that there are several species of closely related species have been grouped taxonomically under one binomial nomenclature.