FISHERY BULLETIN: VOL. 73, NO. 3 



caudal peduncle, depending on the species (Figure 

 53). Cybiosarda has the most inferior foramina, on 

 10 to 12 vertebrae; Orcynopsis has 9 to 10; Sarda 3 

 to 7; and Gymnosarda 6 to 7. Allothunnus has the 

 largest inferior foramina on 7 to 9 vertebrae. 



Infracentral Grooves 



Nakamura and Kikawa (1966) described three 

 types of infracentral grooves on the ventral side of 

 the vertebral centra in tunas. They placed Sarda 

 orientalis in type C, with a single groove, and this 

 is the category of all species of Sarda, Cybiosarda, 

 and Orcynopsis (Figure 54). Gymnosarda (Figure 

 54e) has the type C infracentral grooves on the 

 centra, but the grooves are much deeper and a 

 shallow transverse septum is present in the middle 

 of each groove. Nakamura and Kikawa (1966) did 

 not place Allothunnus in any of the three 

 categories. The precaudal vertebrae of Allothun- 

 nus have type A, with two separate infracentral 

 grooves per centrum, but these are not distinct 

 posteriorly as shown in Figure 54f. Some of the 



17 

 18 

 19 

 20 



0B[ 



m 



Figure 54.-Infracentral grooves on the ventral surface of four 

 vertebrae including the last precaudal and first caudal vertebra 

 in six species of Sardini. a. Cybiosarda elegans, New South 

 Wales, 365 mm FL. h. Orcynopsis unicolor, lsra.e\, 545 mniFL. c. 

 Sarda australis, New South Wales, 407 mm FL. d. Sarda sarda, 

 Tunisia, 504 mm FL. e. Gymnosarda unicolor, Amirante Islands, 

 713 mm FL. f. Allothunnus fallai, Tasmania, 775 mm FL. a, c, 

 and d drawn twice as large as b, e, and f. 



grooves may be covered with a layer of thin bone, 

 especially on the anterior precaudal vertebrae. In 

 all the bonitos, the grooves are very irregular on 

 the first several vertebrae. 



Ribs and Intermuscular Bones 



Pleural ribs are present from the third vertebra 

 posterior to the 18-27th vertebra, depending on the 

 species. Intermuscular bones start on the back of 

 the skull and extend to the 19-39th vertebra. 



Sarda differs from other bonitos in having two 

 cephalic intermuscular bones attached to the 

 exoccipital on each side of the skull (Figures 12, 

 26). One is attached to the center of the exoccipital. 

 The other one is attached to the exoccipital just 

 anterior to the first neural prezygapophysis close 

 to the midline of the skull. Orcynopsis, Cybiosarda, 

 and Allothunnus have the median cephalic inter- 

 muscular bone, but the lateral one is represented 

 only by an unossified ligament. Gymnosarda 

 completely lacks cephalic intermuscular bones and 

 also lacks a ligament in the lateral position. A 

 ligament is present in the comparable position of 

 the median cephalic intermuscular bone. 



Sarda has more pleural ribs than do other 

 genera, 19-24 pair; Cybiosarda has 20, Allothunnus 

 18, Gymnosarda 17, and Orcynopsis 16. These 

 numbers are well correlated with vertebral 

 number except that Cybiosarda has fewer than 

 would be predicted. 



The same general trend is apparent in the 

 number of intermuscular bones but several genera 

 are not in corresponding order. Sarda sarda has 

 the most (36-45 pair) followed by other species of 

 the genus (32-36). Following are Allothunnus 

 (28-29) and Gymnosarda (25-28) with more than 

 expected; Cybiosarda (23-24) with fewer than ex- 

 pected; and Orcynopsis (19-20) with the fewest. 



Caudal Peduncle Keels 



We believe that there is a general evolutionary 

 trend within the Scombridae in the relative 

 development of keels on the caudal peduncle. The 

 Gasterochismatinae and the primitive members of 

 the Scombrinae (Scombrini-mackerels and 

 Scomberomorini-Spanish mackerels) lack sup- 

 porting bony keels and have only external fleshy 

 keels on the caudal peduncle. Starting with the 

 bonitos, bony keels are developed under the larg- 

 est pair of fleshy keels to strengthen and support 

 them. They are developed in two different ways in 



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