CRESSEY ET AL.: COPEPODS AND SCOMBRID FISHES 



FIGURE 5. — Distribution of Scomberomorus lineolatus, S. plurilineatus, S. munroi, and S. niphonius. 



tached to the gill filaments; and several species of 

 Caligus, found in the gill area, mouth, and on the body 

 surface. 



The generally accepted theory that the more primi- 

 tive members of a host group usually harbor more 

 species of parasites than those that evolved later in- 

 dicates the following. Scomberomorus commerson is 

 the most widespread species occurring from the east- 

 ern Mediterranean (recent Suez migrant) eastward 

 throughout the Indian Ocean into the western Pacific 

 Ocean (see Figure 3). Nine species of copepods, from 

 four genera cited above plus two additional genera 

 (Ticxophorus and Brachiella), have been collected 

 from S. commerson. No other species of Scom- 

 beromorus harbors more than seven species and six 

 genera of copepods. Thus, the parasite data indicate 

 S. commerson to be the most primitive member of the 

 Indo- West Pacific Scomberomorus. If the converse is 

 true, the data suggest that S. multiradiatus with only 

 two copepod species is the most advanced (special- 

 ized). 



The data further suggest that the origin of S. com- 

 merson was in the Indo-Australian Archipelago, be- 

 cause all nine species of copepods are reported from 

 specimens in that area with a decrease in the num- 



ber of parasite species to the north and west (Fig. 



7). 



Scomberomorus niphonius is unusual among the 

 Indo- West Pacific members of the genus in its cope- 

 pod parasites. Most Indo-West Pacific Scomberomo- 

 rus are parasitized by P. armatus. Scomberomorus 

 niphonius is commonly parasitized by a closely re- 

 lated species, P. scomberomori, which has more pri- 

 mitive characters than P. armatus, and is apparently 

 specific to S. niphonius. This suggests that S. ni- 

 phonius may be primitive compared with the other 

 Indo-West Pacific species. Scomberomorus nipho- 

 nius might also be considered primitive based on one 

 of its morphological characters (Fig. 4). It is the only 

 species in the genus to have a straight intestine. Most 

 other species of Scomberomorus have two bends (and 

 three sections) to the intestine. One species, S. 

 koreanus, has three bends (and five sections), pre- 

 sumably a specialized condition. 



Two of the 19 specimens of S. niphonius were para- 

 sitized by C. pelamydis (the only Caligus so far 

 reported from it) which is found on several other 

 scombrids, most commonly on species of Sarda. 

 Caligus cybii, closely related to C. pelamydis, has 

 been reported from sue Indo-West Pacific species of 



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