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



Figure 45.-Left opercles of six species of Sardini, external view. a. Cybiosarda elegans, Western Australia, 422 mm 

 FL. b. Orcyncypsis unicolor, Tunisia, 645 mm FL. c. Sarda orientalis, Tokyo, 500 mm FL. d. Sarda australis, New South 

 Wales, 495 mm FL. e. Gymnosarda unicolor, Amirante Islands, 713 mm FL. f. Allothunnus fallai, California, 680 mm 

 FL. 



in Cybiosarda and Orcynopsis than in the species 

 of Sarda. A trace of these ridges is discernible in 

 Allothunnus and the bone is much thinner than in 

 other genera. Gymnosarda (Figure 46e) has no 

 ridges and the entire subopercle is more elongate 

 than in other bonitos. 



Preopercle.-The elongate preopercle is 

 thickened along its inner surface for attachment 

 with the hyomandibula (see Figure 9). The 

 preopercles are similar in Cybiosarda, Orcynopsis, 

 and the species of Sarda (Figure 47a-d). The dorsal 

 projecting arm is somewhat longer and narrower 

 in the species of Sarda than in Cybiosarda and 

 Orcynopsis. As is true of the subopercle, the 

 preopercle of Gymnosarda (Figure 47e) is long and 

 narrow compared to the previous three genera. 

 Allothunnus (Figure 47f) has a preopercle much 

 more similar to Thunnus (de Sylva 1955:17, fig. 28) 



than to other bonitos. It is divided into superior 

 and inferior arms which are approximately equal 

 in length instead of the superior arm being longer 

 than the inferior arm. 



Interopercle.-The interopercle is roughly 

 shaped like an elongate triangle, with a narrow 

 anterior end. Most of the outer surface of the 

 anterodorsal portion of the interopercle is covered 

 by the preopercle. On the inner surface, beneath 

 the middle of the anterodorsal margin of the 

 interopercle, there is a condyle, which articulates 

 with the posterior end of the epihyal and the in- 

 terhyal. The anterior and posterior ends of the 

 interopercle are narrowest in Allothunnus and 

 broadest in Gymnosarda (Figure 48). The thinnest 

 part of the interopercle is along the ventral mar- 

 gin, and a weak fimbriate posterior margin is 

 present in all the bonitos as in Thunnus. 



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