COLLETTE ET AL.: SCOMBROIDEI 



619 



Allothunmis (Fig. 328).— This and the other genera of Thunnini 

 are very similar in appearance and are separated on the basis 

 of pigment patterns. All five genera have similar myomere counts, 

 preopercular spines present and spiny supraorbital crests absent. 

 Allothunrms fallai has 39 myomeres and unique melanophore 

 patterns are present on the mid-ventral surface of the lower jaw 

 along the base of the second dorsal fin. 



Auxis (Fig. 329).— There appear to be two world-wide species 

 with 39 myomeres but there is some variation in pigment pat- 

 tern. The genus is characterized by having melanophores deeply 

 embedded behind the midbrain, cleithral symphysis, along the 

 ventral margin of the tail and melanophores absent from the 

 forebrain. The first dorsal fin is weakly developed and mela- 

 nophores occur along the lateral midline of the tail and on the 

 dorsal margin of the caudal peduncle in some specimens. The 

 profile of the head is blunt and the jaws are short giving the 

 larvae a characteristic ".'iMA/i-look" which is different from the 

 next three genera. 



Euthynnus (Fig. 329).— Two species have 39 myomeres and a 

 third, E. lineatus, has 37. These larvae have slightly longer 

 snouts than other Thunnini and a slight supraoccipital protu- 

 berance. The unique pigment pattern is characterized by me- 

 lanophores occurring on the forebrain, midbrain, cleithral sym- 

 physis, and ventrally, laterally and dorsally on the tail. The first 

 dorsal fin is strongly developed and heavily pigmented. 



Katsuwonus (Vig. 329).— The single species, K. pelamis. has 41 

 myomeres and a reduction in melanophores as they occur only 

 on the forebrain, midbrain, one to three distinct melanophores 

 on the ventral margin of the tail and rarely one or two on the 

 dorsal margin of the caudal peduncle. 



Thunnus (Fig. 329).- All 7 species (Gibbs and Collette. 1967) 

 have 39 myomeres and show the greatest reduction in mela- 

 nophores in the family. Most species can be separated on the 

 basis of melanophores. Thunnus thynmis and T. inaccoyiihavt 

 melanophores on the ventral margin of the tail and the dorsal 

 margin of the trunk and tail. Thunnus ohesus and T. atlanticus 

 have melanophores only on the ventral margin of the tail. Thun- 

 nus alhacares and T. alalunga lack tail melanophores. Thunnus 

 tongol is unidentified. Geographic distribution, time of spawn- 

 ing and internal characters must be used to identify larvae of 

 this genus. We recommend that the following publications be 

 carefully consulted before attempting specific identifications: 

 Matsumoto et al. (1 972), Richards and Potthofr( 1 974), Potthoff 

 (1974, 1975) and Kohno et al. (1982). 



Relationships 



Okiyamaand Ueyanagi (1978) compared a classification based 

 on larval characters of 12 genera of Scombrinae with the clas- 

 sification of Collette and Chao (1975). They selected 13 pre- 

 sumed phylogenetically important larval characters (Okiyama 

 and Ueyanagi, 1978: table 2) and then coded the character states 

 (Table 159). Their dendrogram (Fig. 330) shows four groups. 

 Group A, Scomber and Rastrelliger. corresponds to the tribe 

 Scombrini (Fig. 324). Group B consists only of Gratnmator- 

 cynus. Group C equals the Thunnini (Fig. 324) plus Alloihunnus. 



This interpretation is reasonable on cladistic grounds as dis- 

 cussed in the family section. Group D is a mixture of the Scom- 

 beromorini and Sardini. Okiyama and Ueyanagi admitted that 

 this group is a "heterogeneous assemblage." 



The question of whether or not the billfishes should be con- 

 sidered scombroids has been addressed by Potthoff et al. (ms). 

 They studied osteological developmental features as shown in 

 Tables 160 and 161 and Figs. 331 and 332. Although their re- 

 search is still preliminary because of lack of adequate devel- 

 opmental series for many genera, they conclude that the Istio- 

 phoridae and Xiphiidae should not be placed within the 

 Scombroidei because of three developmental characters which 

 are not shared by any other scombroids. First, all scombroids, 

 except the Istiophoridae and Xiphiidae, have distinctive saddle- 

 shaped ossifications on the vertebrae before the centra are fully 

 formed. Second, development of the cartilaginous neural and 

 haemal spines also is similar in all scombroids, except istio- 

 phorids and xiphiids. Third, scombroids except istiophorids and 

 xiphiids share a primitive and an advanced development of the 

 first and second dorsal and anal fins and their supporting pter- 

 ygiophores. In the primitive development, which is shared by 

 Scombrolabra.x and Scombrini (and which is the basic devel- 

 opmental pattern of percoids), the second dorsal fin, anal fin 

 and pterygiophores develop first from a center anteriorly and 

 posteriorly and the first dorsal fin and pterygiophores develop 

 second, also from a center anteriorly and posteriorly. In the 

 advanced development, which is shared by the Gempylidae, 

 Trichiuridae and Thunnini, the first dorsal fin and pterygio- 

 phores develop first from the anteriormost element in a posterior 

 direction, and the second dorsal fin, anal fin and pterygiophores 

 develop second from a center anteriorly and posteriorly. In the 

 Istiophoridae, the first dorsal fin and pterygiophores develop 

 first from a center anteriorly and posteriorly. When the posterior 

 portion of the first dorsal fin development reaches above the 

 anterior portion of the anal fin, a few anal rays and pterygio- 

 phores develop anteriorly but most are added posteriorly. The 

 second dorsal fin develops only in a posterior direction consec- 

 utive to the first dorsal fin. In Xiphias the second dorsal and 

 anal fins and pterygiophores develop first from a center ante- 

 riorly and posteriorly. Development of the first dorsal fin and 

 pterygiophores then is continuous with the second dorsal fin 

 and in an anterior direction only. 



In addition to their work, one can see the striking differences 

 between billfish larvae and other scombroids simply by review- 

 ing the illustrations of larvae in this report. However, these 

 synapomorphies of istiophorids and xiphiids are not shared with 

 any other group of fishes and so cannot be used as an argument 

 to relate the billfishes to any other taxa. Billfishes have another 

 unique synapomorphy: a specialized organ for heat production 

 located beneath the brain and adjacent to the eyes (Block, 1983). 

 The Scombridae, Istiophoridae and Xiphiidae have a stay on 

 the 4th phary ngobranchial that is absent in other perciforms (G. 

 D. Johnson, pers. comm.). Until further work is completed and 

 other characters thoroughly studied, the billfishes are retained 

 in the Scombroidei. The larval evidence presented indicates a 

 close relationship among the families Scombrolabracidae, Gem- 

 pylidae, Trichiuridae and Scombridae and much more distant, 

 if any, relationship to the Istiophoridae and Xiphiidae. 



