CRESSEY ET AL.: COPEPODS AND SCOMBRID FISHES 



FIGURE 3. — Distribution of Scomberomorus cavalla, S. commerson, and S. sinensis. 



Unicolax appears to be more advanced than Holo- 

 bomolochus by possessing a heavily sclerotized mod- 

 ified seta on the first antenna and having 1 seta rather 

 than 2 setae on the mid-endopod segment of leg 3. 



The highly modified copepod genus Shiinoa (Shiin- 

 oidae) is comprised of three species: Shiinoa occlusa 

 from Indo-West Pacif ic A canthocybium, Grammator- 

 cynus, Scomberomorus, and Gymnosarda and the 

 eastern Atlantic S. tritor; Shiinoa inauris from west- 

 ern Atlantic Scorn beromorus (except S. cavalla); and 

 Shiinoa elagatis from Indo-Pacific Elagatis (Caran- 

 gidae). The first author is describing a fourth spe- 

 cies from the Indian Ocean jack, Caranx malabaricus. 

 Of the three described species S. elagatis with 3- 

 segmented rami of legs 1 and 2 is the most primitive. 

 Shiinoa occlusa from Indo-West Pacific scombrids is 

 intermediate with 3-segmented rami of legs 2 and 3 

 but with fewer spines and setae and reduced body 

 segmentation compared with S. elagatis. Shiinoa in- 

 auris from three of the four western Atlantic Scom- 

 beromorus (all except S. cavalla) is most advanced 

 with only 2 segments in the exopods of legs 2 and 3 of 

 the females and 2 segments in both rami of legs 2 and 

 3 of the males. 



Infestations by the western Atlantic S. inauris and 



its speciation probably did not occur until after the 

 last geologic separation of the eastern Pacific. On 

 scombrids, Shiinoa has differentiated into only two 

 species. Although this genus is recorded from 1 spe- 

 cies of Scomberomorus, the highest rates of infesta- 

 tion among scombrid hosts are in Grammatorcynus 

 and Gymnosarda. Shiinoa occlusa, from Indo-West 

 Pacific scombrids, is more primitive than the western 

 Atlantic S. inauris, indicating the latter' s probable 

 derivation from Indo-Pacific stock. 



The presence of the highly specialized siphono- 

 stome copepod parasite, P. buccata, on all species of 

 American Scomberomorus with relatively high infes- 

 tation rates (30- 63%) indicates that this parasite was 

 present before the separation of Atlantic and eastern 

 Pacific Oceans, but, in spite of the present isolation, 

 the two populations have not differentiated (unlike 

 the three Holobomolochus species). 



From this it appears that dispersal and some specia- 

 tion of American Scomberomorus occurred prior to 

 their being parasitized by bomolochid and shiino- 

 id copepods. 



The evidence derived from an analysis of the cope- 

 pods parasitic on the six American Scomberomorus 

 species suggests the following sequence of events: 



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