610 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 328. Lateral views oi Allolhunnus fallai larvae (upper) 5.7 mm NL and (lower) 6.9 mm SL modified after Watanabe et al. (1966). 



anterior portion of the branchiostegal membrane. Istiophorus 

 platypterus has an elongate snout, small eyes, and a relatively 

 small head depth. Melanophores appear characteristically on 

 the posterior peripheral area of the gular membrane. However, 

 there are some sailfish larvae which lack gular melanophores, 

 and these are thought to belong to a different population. Tel- 

 rapturus angiistirosths larvae of small size are similar to M. 

 mazara, but the anterior edge of the orbital rim does not project 

 forward and melanophores occur on the branchiostegal mem- 

 brane. 



In the Atlantic, specific differences are not nearly as clear. 

 Makaira indica larvae have not been identified although adults 

 are known. Makaira nigricans larvae are indistinguishable from 

 Makaira mazara and are characterized by the short snout, an- 

 terior projection of the orbital rim, and a lack of gular mela- 

 nophores. Tetrapturus pjluegeri larvae are very similar to T. 

 angustirostris and characteristically possess melanophores on 

 the branchiostegal membrane. It is also a winter spawning species, 

 whereas the others are spring and summer spawners. Tetrap- 



turus albidus larvae are very similar to T. audax in the profile 

 of the head and possessing melanophores on gular membranes. 

 Tetrapturus georgei larvae are unknown, and T. he/one have 

 been briefly described without mention of the presence or ab- 

 sence of branchiostegal melanophores. A great amount of time 

 has been spent attempting to separate Atlantic /. platypterus 

 and T. alhidus with no success (Richards, 1974). Both have 

 relatively long snouts and pigmented gular membranes. Vari- 

 ation in gular and branchiostegal pigmentation has been de- 

 scribed in Atlantic T. pfluegeri (Ueyanagi, 1974b). 



The elongate upper jaw, a characteristic of istiophorid fishes, 

 is also found in the fossils Palaeorhynchus and Blochius which 

 are thought to be the ancestral forms (Fierstine, 1972); hence, 

 the elongate upper jaw may have phyletic meaning. When the 

 character of upper jaw length compared to body length is ex- 

 amined during the larval period, clear differences were observed 

 (e.g., longer upper jaw in Istiophorus and Tetrapturus, and short- 

 er in Makaira). Adult T. angustirostris possess an especially 

 short snout among the species in the genus; elongation of the 



Fig. 329. Lateral views of scombrid larvae from top to bottom: all drawn by J. Javech, Gulf of Mexico, OREGON II. Cr. 1 17, Auxis^p-. 5.0 

 mm NL, Sta. 34463; Euthynnus allelleralus, 6.2 mm SL, Sta. 34463; Kalsuwonus pelanus. 5.9 mm SL, Sta. 34448; and Thuimus thynnus. 6.0 

 mm SL, Sta. 34497. 



