Regalecidae is differentiated from the related Trachipteridae most easily by the long pelvic fins consisting of only one fin ray.

One way to differentiate Regalecus glesne from Agrostichthys parkeri, the only other species in the family Regalecidae, is the number of gill rakers: while R. glesne has 40-58, A. parkeri has 8-10. R. glesne has no dorsal spines, A. parkeri has many. Also, while R. glesne is subtropical, distributed in Bermuda and both coasts of Florida, from Southern California to Chile, and in the Caribbean, A. parkeri is found in Southern Hemisphere temperate waters (Robins and Ray, 1986; Schmitter-Soto, 2008).