496 



ONTOGENY AND SYSTEMATICS OF FISHES-AHLSTROM SYMPOSIUM 



Fig. 263. Scanning electromicrographs of epithelium of juvenile dolphins and cobia at various magnifications. (A) Coryphaena hippurus, 28 

 mm SL, 15 x; (B) C. hippurus. 28 mm SL, 360 x; (C) Rachycentron canadum. 30 mm SL, 15 x; and (D) R. canadum. 80 mm SL, 360 x. 



the nasal bones. The nasal bones first appear as separate struc- 

 tures, but prior to or during flexion, they become fused anteriorly 

 by a median bony bridge. This modified nasal structure then 

 develops the various ornamentations that characterize mala- 

 canthid and branchiostegid larvae. At transformation, the bony 

 bridge begins to fragment and is eventually entirely resorbed, 

 so that the nasal bones once again become completely separate. 

 I know of no other example in fishes of transient ontogenetic 

 fusion of nasal bones. This unique synapomorphy, in conjunc- 

 tion with the other shared larval specializations, cogently sup- 

 ports the hypothesis that malacanthids and branchiostegids are 

 sister groups. Classification of the two lineages of tilefishes as 

 subfamilies of the Malacanthidae seems an appropriate way to 

 express this relationship. 



The evolutionary relationships of the dolphins, Coryphaen- 

 idae, have remained uncertain, but the family has usually been 

 placed close to the Carangidae as have the Echeneididae and 

 the monotypic Rachycentridae. Examination of the larvae of 

 these groups during this investigation and subsequent consid- 

 erations of adult morphology have led to further resolution of 

 the interrelationships of these families (Johnson, Abstracts of 

 1983 ASIH Annual Meeting). This final example provides the 



most convincing illustration of the importance of larval char- 

 acters to studies of phylogeny among percoids. Consequently I 

 discuss it in considerable detail. 



Freihofer (1978) noted that the Nematistiidae, Carangidae, 

 Coryphaenidae, Rachycentridae and Echeneididae share a unique 

 specialization in the lateralis system on the snout— an anterior 

 extension of the nasal canal consisting of one (Nematistiidae) 

 or two prenasal canal units, with one (Nematistiidae and Ca- 

 rangidae) or both (remaining three families) surrounded by tu- 

 bular ossifications. In addition, they share small, adherent cy- 

 cloid scales. Based on two presumed synapomorphies, then, 

 these five families constitute a monophyletic group, hereafter 

 referred to as the carangoids. 



Three synapomorphies unite the Carangidae, Coryphaenidae, 

 Rachycentridae and Echeneididae as a monophyletic group. 

 These four families lack the bony stay (Potthoff, 1975) posterior 

 to the ultimate dorsal and anal pterygiophores found in almost 

 all other percoids (see Table 1 20), have two prenasal canal units 

 and have a lamellar expansion along the anterior margin of the 

 coracoid. Nematisttus, placed in separate family by Rosenblatt 

 and Bell (1976), is apparently the sister group of these four 

 families (see cladogram. Fig. 276, in Smith-Vaniz, this volume). 



