Classification depends upon comparison of many characters, the ranges of which frequently overlap at the extremes however lemniscal length is a relatively consistent difference among species.

[1] Intermediate hosts infected with cystacanths (a larval or resting stage for acanthocephalans) include the aquatic isopods Asellus forbesi and Licreus lineatus in Jackson County, Illinois.

[5] Females are between 20 and 52 mm long and with a subterminal genital pore and males usually have two testes, which is unique in the Fessisentis genus.

[6] F. friedi has been found infecting the grass pickerel (Esox americanus)[5] and the White sucker (Catostomus commersoni).

[1] F. necturorum was found parasitizing the Marbled salamander (Ambystoma opacum) larvae near Athens, Georgia and the Gulf Coast waterdog (Necturus beyeri) from southern Louisiana.

Proboscis receptacle wall musculature has 2 layers of tubular bundles with peripheral contractile fibers and a central noncontractile cytoplasm characteristic to other species in the genus.

Fessisentis species exclusively parasitize, as adults, North American gilled salamanders and freshwater fishes.