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



THUNNUS 



GYMNOSARDA 



SARDA 



CYBIOSARDA 



ALLOTHUNNUS 



ORCYNOPSIS 



ACANTHOCYBIUM 



Figure 55.— Dorsal view of last seven or eight preural centra to show structure of bony caudal keels in the five 

 genera of Sardini plus Acanthocybium and Thunnus representing a more primitive (Scomberomorini) and a 

 more advanced tribe (Thunnini) respectively. 



the bonitos. Orcynopsis, Cybiosarda (Figure 55), 

 and Allothunnus have low keels running the en- 

 tire length of the vertebrae involved. Sarda and 

 Gymnosarda have wider keels, as in the higher 

 tunas, but they are divided into two segments on 

 each vertebra, one on the anterior part of the ver- 

 tebra and one on the posterior part. The higher 

 tunas {Thunnini- Auxis through Thunnus) have a 



wide flattened plate that acts as a single func- 

 tional unit over several vertebrae. 



Within the bonitos, there are minor differences 

 as to which vertebrae bear the bony caudal keel. 

 Counting anteriorly from preural centrum one, 

 Orcynopsis differs from Cybiosarda in having 

 keels concentrated on the fourth to sixth preural 

 vertebrae instead of on the fifth to seventh. 



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