Fku're 9. — Subopercle of (left) Thurmus thyrin}i.i, (right) 

 T. (ilidunija. Same specimens as in fig. (i. 



We are unable to confirm two other characters 

 mentioned by Kishinouye (1923: 325, 327). In 

 Japanese T. thi/nnus the posterior margin of the 

 interopercle was described as being convex, whereas 

 in other Japanese tunas it is nearly straight. In our 

 material the shape of the mai-gin is variaV)le; most of 

 the species have both types and variants thereof. 

 Kishinouye also described a groove for blood vessels 

 along the dorsolateral edge of the ceratohyal. The 

 groove was present in T. thi/nnus, T. alalunga, and 

 T. obesus but hardly visible in T. albacarrs. This 

 grove is present in all species and is generally more 

 apparent in larger specimens. In small specimens 

 of most species the groove is indistinct or absent. 



Pectoral and Pelvic Girdles 



The pectoral girdle is composed of a series of bones 

 connecting the skull and the pectoral fin. The two- 

 armed supratemporal, not really a functional part 

 of the pectoral girdle, is closely applied to the skin 

 beside the otic region of the neuroeranium. A larger, 

 also two-armed, posttemporal articulates with the 

 skull, followed by a supracleithrum and the large, 

 curved, bladelike cleithrum. Baudelot's ligament 

 runs from the supracleithrum to the basioccipital. 

 From the posterior margin of the supracleithrum 

 extend two flattened postcleithra, the second of 

 which has an attenuated posteriorly directed process. 

 The long curved blade of the cleithrum forms a thin- 

 walled trough that opens posteriorly. The thick- 

 ened, somewhat rectangular scapula is borne dorsallv, 

 on the mesial side. Below the scapula, the blade- 

 like coracoid is attached. The lower, posterior end 

 of the scapula and the uppermost posterior edge of 



the coracoid are thickened and flattened; they form 

 articular surfaces for four (iterygials, on which the 

 fin rays are borne. 



The pelvic girdle includes a pair of winglike basi- 

 pterygia that join posteriorly in the median line. 

 Anteriorly each bone has a flattened lateral wing 

 and a long narrow mesial process. Posteriorly a 

 long mesial process extends between the fin rays. 

 There are no pterygials. 



No differentiating characters are apparent in cither 

 the pectoral or the pelvic girdle. 



Vertebral Column 



General descriplion. — Important papers describing 

 the vertebral column in species of Thunnus include: 

 Starks (1910), Kishinouye (1923), Frade (1932), 

 Godsil and Byers (1944), Godsil and Holmberg 

 (1950), Clothier (1950), de Sylva (1955), and 

 Nakamura (1965). 



The vertebral column usually has 39 vertebrae, 

 including the hypural plate. The first vertebra is 

 articulated firmly with the rear of the skull. Neural 

 arches and spines are present on all except tlio 

 hypural plate. The spines are erect and laterally 

 flattened on the first six vertebrae. On the seven 

 vertebrae anterior to the hypural plate, both the 

 neural and haemal spines arc wide and depressed 

 and lie on top of the next posterior centrum, forming 

 a strong and rigid tail section. Laterally directed 

 transverse processes (parapophyses) appear as small 

 projections on the third vertebra, become longest 

 and broadest on about the sixth, shorter and more 

 canted on the next two or so, and usually become 

 both longer and ventrally directed on the eighth or 

 ninth. By the 10th or 11th vertebra, the first 

 closed haemal arch is formed by the meeting of the 

 distal ends of the parapophyses. The ventral ends 

 of the haemal arches become progressively longer, 

 forming haemal spines. Ribs are attached, begin- 

 ning with the 3d vertebra, to each parapophysis 

 or to the end of each haemal arch or spine until the 

 18th or 19th vertebra. Posteriorly, haemal spines 

 are present, but ribs are absent. Dorsal to the ribs, 

 intermuscular bones (epipleurals) articulate either 

 on the neural arch or the centrum of each of the 

 \ertebrae from the 1st to the 31st. 



Beginning at the 12th to 18th vertebra, each 

 haemal arch bears on each side a process directed 

 obliquely ventrad which has been called a haemal 

 prez.ygapophysis (de Sylva, 1955). On suc'ceeding 

 vertebrae this process is longer, then shorter and 



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