COLLETTE and RUSSO: SPANISH MACKERELS 



and queenslandicus, have a prominent truncate 

 process. 



BASICRANIAL REGION.— This region con- 

 sists of the parasphenoid, basioccipital, and ex oc- 

 cipital bones, and forms the posteroventral base 

 of the skull. 



Parasphenoid. — The parasphenoid is a long 

 cross-shaped bone (Figs. 17-19) which articulates 

 with the vomer anteriorly and forms the ventral 

 axis of the skull. The lateral wing of the para- 

 sphenoid extends dorsolaterally along the ventral 

 ridge of the prootic bones on either side, and has a 

 pointed end which forms part of the antero ventral 

 wall of the posterior myodome. Posteriorly, the 

 parasphenoid bifurcates into two lateral flanges 

 which attach dorsally to the corresponding pos- 

 teroventral flanges of the basioccipital bone and 

 surround the posterior opening of the posterior 

 myodome. A ventrally projecting median keel is 

 present in the area anterior to the origin of the 

 lateral flanges. In ventral view, the general 

 characteristic of the parasphenoid is a gradual 

 narrowing of the bone from anterior to posterior. 

 The broadest portion of the parasphenoid is lo- 

 cated usually at or before the tip of the V-shaped 

 joint with the vomer. Broad parasphenoids are 

 also present in Acanthocybium and the bonitos, 

 Sardini (Collette and Chao 1975). In lateral view 

 (Figs. 14-16), the parasphenoid forms the ventral 

 border to the orbits and connects with the lateral 

 ethmoids, basisphenoid, prootics, and basioccipi- 

 tal bones dorsally. 



The shaft of the parasphenoid is distinctly 

 wider in seven species: S. commerson (Fig. 17a), 

 lineolatus, munroi (Fig. 17b), niphonius, queens- 

 landicus, semifasciatus, and sinensis. Devaraj 

 (1977) included S. cavalla along with S. lineola- 

 tus and S. commerson as having a broad para- 

 sphenoid, based on Mago Leccia (1958). We find S. 

 cavalla to have a broader parasphenoid than some 

 members of the regalis species group but not as 

 broad as in the group of seven species listed above. 



Basioccipital. — The basioccipital is the most 

 posteroventrally located bone of the skull. It is 

 shaped like an inverted U with lateral flanges on 

 either side of the skull and forms the roof and 

 lateral walls of the posterior myodome. Anterior- 

 ly, the basioccipital is attached to the prootic 

 bones and dorsally with the exoccipital bones. Its 

 lateral flanges expand ventrally to meet the flat 

 posterior flanges of the parasphenoid. Posterior- 



ly, the lateral flanges fuse to form a circular 

 margin in a slightly backward oblique position 

 and attach to the margin of the first vertebral 

 centrum. There are a variable number of small 

 pores in a shallow depression on the lateral 

 surfaces of the basioccipital. This depression is 

 deepest in S. sinensis but does not approach 

 the basioccipital depression characteristic of the 

 bonitos, Sardini (Collette and Chao 1975). 



Exoccipital. — The exoccipitals connect the 

 skull to the first vertebra dorsally. The exoccipi- 

 tal articulates with the epiotic and supraoccipital 

 bones anterodorsally, the intercalar laterally, 

 and with the other exoccipital posterodorsally In 

 ventral view, the exoccipital articulates with the 

 prootic anteriorly, basioccipital medioventrally, 

 and intercalar laterally. In posterior view, the 

 foramen magnum is framed by the exoccipitals. 

 Laterally, there are two foramina. The small 

 anterior glossopharyngeal foramen (Allis 1903) 

 lies close to the posterior border of the prootic. 

 The large posterior vagal foramen lies just under 

 the overhanging shelf formed by the posterior 

 margin of the exoccipital. Dorsally, a small fora- 

 men which opens into the brain cavity is present 

 at the medioposterior corner of the exoccipital. 



Branchiocranium 



The branchiocranium is divided into five sec- 

 tions: mandibular arch, palatine arch, hyoid arch, 

 opercular apparatus, and branchial apparatus. 



MANDIBULAR ARCH. —The mandibular arch 

 is composed of the upper jaw (premaxilla, maxil- 

 la, and supramaxilla) and the lower jaw (dentary, 

 angular, and retroarticular). Teeth are borne on 

 the premaxilla and dentary, and the number of 

 teeth on these bones is a useful taxonomic char- 

 acter (see Dentition section). 



Dentition. — Large, triangular, laterally com- 

 pressed teeth are present in the upper and lower 

 jaws of Scomber omor us. Acanthocybium has sim- 

 ilar teeth that are a little blunter and more 

 tightly packed. Grammatorcynus has long thin 

 teeth that are slightly compressed laterally. Bo- 

 nitos have conical teeth that are larger than the 

 conical teeth of the higher tunas (Thunnini). 

 Tooth replacement in Scomberomorus cavalla 

 was studied by Morgan and King (1983). The 

 number of jaw teeth in Scomberomorus varies 

 widely with a range of 5-39 in the upper jaw, 4-37 



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