FISHERY BULLETIN: VOL. 81, NO. 2 



FIGURE 2.— Distribution of Atlantic and eastern Pacific species of Scomberomorus. 



the last exopod segments of legs 2-4 bear a number of 

 plumose setae, heavily sclerotized spines, and short- 

 er nonplumose setae with armature intermediate to 

 that on spines and setae. Long plumose setae (adap- 

 tations for free swimming) are primitive, whereas 

 heavily sclerotized spines (adaptations for attach- 

 ment) are advanced characters. The three Holobomo- 

 lochus from Scomberomorus show a transition in the 

 numbers of each of these character states. Holo- 

 bomolochus asperatus (parasite of S. cavalla) bears 

 1 8 long plumose setae and 7 sclerotized spines on the 

 last exopod segments of legs 2-4. The same append- 

 ages of H. nudiusculus (on eastern Pacific Scom- 

 beromorus) bear 16 plumose setae, 2 intermediate 

 setae/spines, and 7 spines. The same appendages of 

 H. divaricatus (on all western Atlantic Scomberomo- 

 rus except cavalla) bear 14 setae, 4 intermediate 

 setae/spines, and 7 spines. This transition in de- 

 creased numbers of long plumose setae and increase 

 in intermediate setae/spines within these three para- 

 site species suggests H. asperatus to be the most 

 primitive, H. nudiusculus intermediate, and H. di- 

 varicatus to be most advanced. If the hosts reflect the 

 phylogeny of the parasites, then this suggests that S. 

 cavalla is the most primitive; the two eastern Pacific 



species — S. sierra and S. concolor — are interme- 

 diate; and the three western Atlantic species — S. 

 regalis, S. maculatus, and S. brasiliensis — are the 

 most advanced of the American species of Scomber- 

 omorus. 

 Holobomolochus has 23 currently recognized spe- 

 cies in the western Atlantic and eastern Pacific and 1 

 species from the eastern Atlantic (a species from In- 

 dia is not a Holobomolochus, as reported by Pillai 

 1973). Unicolax ciliatus, a species of another bomo- 

 lochid genus, is found on 9 species of Scomberomo- 

 rus in the Indo-West Pacific and on S. tritor in the 

 eastern Atlantic. Four remaining species of Unicolax, 

 including Atlantic and eastern Pacific species, are 

 found only on non-Scomberomorus scombrids. This 

 parasite distribution and host affiliation suggest that 

 Holobomolochus was already well established on 

 American Scomberomorus before the appearance of 

 Unicolax in this area. Based on the evidence that U 

 ciliatus has not undergone further speciation on 10 

 Scomberomorus species despite the geographic isola- 

 tion of one of those species (S. tritor from the eastern 

 Atlantic) and the presence of Holobomolochus on the 

 American Scomberomorus, it can be assumed that 

 Holobomolochus is older than Unicolax. 



234 



