ALA 



THY 



OBE 



ALB 



ATL 



TON 



Figure 12. — Left lateral view of vertebrae of Thunnus species, 

 showing development of anteriorniost haemal pre- and post- 

 zygapophyses. ALA— vertebrae 13-16, ALB— 14-16, 

 ATL— 14-18, OBE— 14-17, THY-14-16, andTOX-14-17. 



it may range from almost perpendicular to a 60° 

 angle (fig. 11). The shape of the first haemal arch 

 and the dimensions of its bony parts vary consider- 

 ably, but in T. atlanticus, T. tonggol, and T. maccoyii 

 the bony portions are thinner and the sides more 

 bowed than in the other species (fig. 10). 



As shown by Yabe et al. (1958), by Matsumoto 

 (1963), and by Yoshida (1965), the heamal spine of 

 the first caudal vertebra is always laterally flattened 

 and winglike in T. alalunga but in the other species 

 resembles the other haemal spines and is not flattened. 



The length of the haemal prezygapophyses and 

 the distance of their origin from the centrum vary 

 among the species of Thunnus. In T. alalunga the 

 haemal prezygapophyses all originate at the centrum 

 or extremely close to it. Correlated with this, the 

 anterior haemal postzygapophyses are relatively 

 short (fig. 12). In the other species the anterior 

 haemal prezygapophyses arise from the sides of the 

 haemal arches of 3 to 12 vertebrae before they begin 

 to arise from the centra, and the posterior haemal 

 postzygapophyses are relatively longer. In T. ala- 

 lunga, T. ohesus, T. nmccoyii, and T. thynnus the 

 haemal prezygapophyses arise high on the neural 

 arch, so that only the first two or three at most can 

 be regarded as clearly on the arch. Correspondingly, 

 the associated haemal postzygapophyses hardly dif- 

 fer in length from those on the posterior vertebrae. 

 By contrast, in T. atlanticus, T. albacares, and T. 

 tonggol the haemal prezygapophyses arise far more 

 ventrad on the haemal arch, from one-fourth to 

 one-half the distance to the ventral tip, and there is 

 no question that at least five (usually more) are 

 definitely on the arch, not on the centrum. The 

 associated haemal postzygapophyses in these species 

 are longer than in the other three, although less so 

 in T. albacares than in T. atlanticus and T. tonggol. 

 In T. atlanticus and T. tonggol the longest haemal 

 postzygapophyses are equal to or longer than the 

 length of the centra; in T. albacares they may be 

 about three-fourths the centrum length. 



The species differ in the development of the ventro- 

 lateral foramina that are found on some or all of the 

 20th to the 33d vertebrae (fig. 13). These foramina 

 are best developed anteriorly and in this region 

 appear to arise through the formation of a bony strut 

 from the haemal postzygapophyses to the dorsal 

 part of the haemal arch. They diminish in size 

 posteriorly and are absent on the last several ver- 

 tebrae. In T. atlanticus, T. albacares, and T. tonggol 

 the anterior openings are large, longer than wide, 



ANATOMY AND SYSTEMATICS OF TUNAS 



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