[3] Even with its distinctive, point-like long nose, the longnose butterflyfish still can easily be confused with its more common cousin F. flavissimus.

F. longirostris has a compressed yellow body with a black triangular region on its head, and as the name implies, a long, silvery snout.

In comparison, F. flavissimus has more dorsal spines, lacks the black spots, and its operculum is more curved.

[4] Rarely, F. longirostris can be found in an all-black form, as well,[5] or the yellow portion may be brown.

[2] F. longirostris is a diurnal omnivore,[6] feeding mostly on small crustaceans, tube feet of echinoderms and sea urchins, and polychaete tentacles.