COLLETTE and CHAO: SYSTEMATICS AND MORPHOLOGY OF THE BONITOS (SARDINI) 



d e f 



Figure 31.— Left maxillae of six species of Sardini, external view. a. Cybiosarda elegans, New South Wales, 355 mm FL. b. Orcynopsis 

 unicolor, Tunisia, 645 mm FL. c. Sarda australis. New South Wales, 407 mm FL. d. Sarda sarda, Tunisia, 504 mm FL. e. Gymnosarda 

 unicolor, Truk Islands, 696 mm FL. f. Allothunnus fallai, California, 680 mm FL. 



the maxillae of Cybiosarda and Orcynopsis are 

 more pointed than in the other bonitos. 



Supramaxilla.-The supramaxilla covers the 

 posterior part of the maxilla and is partly covered 

 anteriorly by the lachrymal (see Figure 9). It has a 

 flat oval posterior main body and an anterior 

 process which forms a shelf on the inner surface of 

 the bone that continues as a ridge posteriorly. 

 Allothunnus has a smoother dorsal margin and a 

 more gradual transition between the process and 

 the body giving the bone a more triangular shape 

 (Figure 32h). The posterior edge of the 

 supramaxilla of Gymnosarda is more curved and 

 the anterior process is blunter (Figure 32g). Or- 

 cynopsis has a much deeper main body than 

 Cybiosarda. Godsil (1954) used the width of this 

 bone (called auxiliary maxillary) to separate Sar- 

 da chiliensis from 5. orientalis in the eastern 

 Pacific. He found the bone to be much narrower in 

 relation to length in S. orientalis (ratio of width to 

 length 4.1-4.4) than in northeast Pacific S. chilien- 

 sis (ratio 3.0-3.1). We also found that the main 

 body of the supramaxilla is broader in .S. chiliensis 

 and narrower in S. orientalis. There do not appear 

 to be any significant differences between 

 northeast and southeast Pacific populations of S. 

 chiliensis or between Indo-West Pacific and east- 

 ern Pacific S. orientalis in this character. Sarda 

 sarda and 5. australis have the supramaxilla in- 

 termediate in width between the wide bone 

 present in S. chiliensis and the narrow bone in 5. 

 orientalis. 



Dentary.-The dentary divides posteriorly into a 

 dorsal dentigerous branch and a ventral branch, 



which are usually about equal in length, although 

 the ventral branch is slightly longer in Gym- 

 nosarda and Allothunnus and sometimes in Sarda 

 (Figure 33e, f). Allothunnus has a row of 

 numerous (40-50) tiny teeth on the dentary while 

 the other genera have fewer (10-25) strong conical 

 teeth. The number of teeth varies among genera 

 and species (Table 6). The shape of the anterior 

 margin of the dentary can be used to divide the 

 bonitos into three distinct groups. The anterior 

 margin of the bone forms an acute angle with the 

 dentigerous dorsal margin in Sarda, and there is a 

 notch present at the upper portion of the anterior 

 margin. The notch is deeper and located in the 

 middle of the margin in Allothunnus (Figure 33f). 

 Cybiosarda, Orcynopsis, and Gymnosarda lack an 

 anterior notch (Figure 33a, b, e). Another notch is 

 present in Gymnosarda, on the anterior part of the 

 ventral margin; there is a slight depression in this 

 position in the other genera of bonitos. In overall 

 shape and size, the dentary of Sarda is more elon- 

 gate, especially that of S. orientalis. The angle 

 between the dorsal and ventral arms of the den- 

 tary is slightly greater in Gymnosarda. The dorsal 

 branch is wider, flatter, and thinner in Allothun- 

 nus. 



Angular and Retroarticular.— The triangular 

 anterior end of the angular (frequently called ar- 

 ticular) fits into the dentary anteriorly (Figure 9). 

 Allothunnus has the most elongate angular 

 (Figure 34f). The strongest angular is found in 

 Gymnosarda (Figure 34e) followed by Cybiosarda 

 and Orcynopsis (Figure 34a, b). An anteriorly 

 projecting spine is present on the ventral edge of 

 the angular. This spine is thin and weak in 



557 



