- Strong bill, flat-oval in cross-section
- One large keel on caudal peduncle
- Pelvic fins absent
Istiophoridae differ in having a bill that is round in cross section (vs. flat-oval); pelvic fins present (vs. absent); 2 keels on each side of caudal peduncle (vs. 1 median keel on either side); a small interdorsal space (vs. large (in adults)) and a shallow notch on both upper and lower origins of caudal fin (vs. deep notches).
Belonidae differ in having both jaws prolonged (vs. upper jaw prolonged); dorsal and anal fins single (vs. double) and similar in size and shape (vs. different); pectoral fins not falcate (vs. falcate) (except in Ablennes) and pelvic fins present (vs. absent).
There is 1 species in the Xiphiidae genera, Xiphiidae gladius, which can be defined from similar families in the section above.