The Longnose Butterflyfish (Forcipiger longirostris) is bright yellow, with the upper half of the head and nape black and the lower half white. There is a black spot on the anal fin, just below the base of the caudal fin. The Longnose Butterflyfish has a very long snout and a mouth with almost no gape. Length may reach 22 cm. The only other Forcipiger species, the generally more common Forcepsfish (Forcipiger flavissimus), is very similar in color to the Longnose Butterflyfish (with which it was long confused; see Randall and Caldwell 1970), but the Forcepsfish has a distinctly shorter snout, has a mouth with a distinct gape (hence forceps-like), and lacks the blackish dots that are present on the chest of the Longnose Butterflyfish. Some Longnose individuals are entirely dark brown. The Longnose Butterflyfish occurs from East Africa to Polynesia; the Forcepsfish occurs from East Africa to Central America and Mexico. (Randall et al. 1997)
Several other species of butterﬂyﬁshes (family Chaetodontidae) have elongate jaws and feed on a wide range of predominantly attached, benthic invertebrate prey and some free-living, mobile prey. It is thought that the ‘‘manipulation’’ method is used by butterﬂyﬁshes to grip and remove pieces from polychaetes, nemerteans, corals, ascidians, echinoids, hydroids, and other attached prey. Suction feeding is thought to be used when preying upon mobile prey such as calanoid copepods, amphipods, and crab larvae, which are ingested intact. In contrast to other chaetodontids studied, detailed observations in Hawaii and Moorea suggest that the Longnose Butterflyfish, the longest-jawed of the butterflyfishes, is a specialized predator of mobile decapod shrimps, particularly the elusive caridians that live within coral reefs. All five butterfly species studied by Ferry-Graham et al. (2001a) utilized a combination of suction and ram when feeding on brine shrimp in the lab, but Longnose Butterflyfish exhibited a ram contribution to the strike that was more than twice that seen in any of the other species, permitting this species to initiate strikes from the greatest initial predator-prey distance. Longnose Buterflyfish are known to possess a major structural novelty in the feeding mechanism that permits anterior movement of the entire jaw apparatus. The ability to feed successfully on elusive prey appears to be related to exceptional jaw protrusion, resulting in greater use of ram during prey capture. This ability to protrude long, slender jaws toward the prey may allow a Longnose Butterflyfish to move its jaws without detection close enough to a potential prey item to permit the effective use of suction. Interestingly, of 18 butterﬂyﬁsh species examined in Moorea (French Polynesia), the congeners F. ﬂavissimus and F. longirostris exhibited the broadest and narrowest diets, respectively. (Ferry-Graham et al. 2001a,b and references therein)
Boyle and Tricas (2011) studied the kinematics of sound production in both Forcipiger species and suggested that correlations within both species between aspects of acoustic signals and size and condition variables that may be related to resource holding potential during social encounters could allow Forcipiger sounds to function as “honest” social signals.