P. cornuta belongs to the Polydora species complex, so it is important to carefully separate P. cornuta from its very similar looking congeners. Other spionid worms, which might be confused with P. cornuta, may also be found in beach collections. Two diagnostic characters of P. cornuta allow it to be distinguished from related species under a dissecting microscope. The easiest feature to see is a conical structure at the extreme posterior end of the worm (Fig. 10a). The other unique feature is a bifid prostomium (Fig. 10b) (a.k.a. P. ligni, [Smith, 1964]).