tic has only one species of Strongylura — S. sene- 

 galeTisw — and it is confined to the Gulf of Guinea. 

 The western Indian Ocean has only one Strongy- 

 lura — S. leiura — a large offshore species infested 

 (rarely) with L. tylosuri and apparently never 

 with L. helones. L. helones probably will be found 

 to occur on S. senegalensls, so part of the distri- 

 butional gap will be filled in. There does, however, 

 appear to be a real gap in the distribution of 

 L. helones that tends to divide the worldwide 

 population. Perhaps detailed analysis of geo- 

 graphic variation in L. helones will provide 

 morphological support for this geographical two- 

 population hypothesis. The ovigerous females from 

 the Atlantic and the Indo-West Pacific show a 

 difference in total length (See discussion of intra- 

 specific variation in copepods and fig. 187). 



As has been noted previously, the widespread 

 Parabomolochus hellones is replaced by two spe- 

 cies in the eastern Pacific — the closely related P. 

 constrictus and the more distantly related P. ensi- 

 culus (fig. 184). The Eastern Pacific Barrier, so 

 important in blocking the distribution of shore 

 fishes (Briggs, 1961), seems to operate as effec- 

 tively within this genus of needlefish copepods. 



Parabomolochus hellones appears to be in the 

 process of being replaced in the eastern Indian and 

 western Pacific Oceans by P. sinensis and the two 

 species of Nothohomolochus. This replacement is 

 partially apparent from a comparison of the dis- 

 tribution of Parahomolochus (fig. 184) with 

 N othohonwlochus (fig. 185). In the western Pa- 

 cific, P. hellones is common in Japan and Australia, 

 between the 75° and 80° F. isotheres (23.9° C. and 

 26.7° C— Hutchins and Scharff, 1947) , whereas the 

 other three bomolochids are common in the trop- 

 ical waters. Relative abundance of P. hellones also 

 differs from that of the other bomolochids (tables 

 4 and 5) . P. hellones is very abundant in the west- 

 ern Atlantic (infestations ranging up to 42 per- 

 cent). It is also equally abundant on most hosts 

 in the Gulf of Guinea and Mediterranean Sea. 

 However, N. gibher has largely replaced P. hel- 

 lones on one host — Belone svetovidovi. In the Indo- 

 West Pacific, P. sinensis and the two species of 

 Nothohomolochus replace P. hellones on some 

 hosts, particularly ^6Zen«.es hiams and Platyhelone 

 argalus in the western and southern Pacific. Per- 

 haps P. sinensis and tlie two species of Nothoho- 

 molochus evolved more recently and have begun 



to replace the older Parahomolochus hellones in 

 the warmer parts of the Indo-West Pacific 

 oceans. 



The distributional maps of ergasilid copepods 

 (fig. 186) and their fresh- water needlefish hosts 

 (fig. 180) may also be compared. With one excep- 

 tion, the ranges of the host species are greater 

 than those of their ergasilid coi:)epods. The excep- 

 tion is the presence of what we have called Ergasi- 

 lus orlentalis on Potamorrhaphifi in the Amazon 

 Basin and on Strongylura incisa from Arnhem 

 Land, Australia. We do not believe that this is a 

 widespread species, but Cressey has been unable to 

 discover any significant differences between the 

 two populations; for the present we let this dis- 

 tributional pattern stand. 



Probably the most widely distributed ergasilid 

 copepod considered here is Ergasilus coleus. 

 This copepod has been collected on three different 

 hosts: the fresh-water Xenentodon. cancila. from 

 India; the estuarine Strongylura strongylura 

 from India, Borneo, and the Philippine Islands; 

 and the primarily marine S. urviZlii from the 

 Philippines. This extensive distribution argues for 

 either a greater degree of salt tolerance than is 

 usually found in ergasilids or an old distributional 

 pattern dating back to when the fresh waters of 

 southeast Asia, Borneo, and the Philippines were 

 connected, permitting the transfer of fresh-water 

 fishes and their parasites. 



Intraspecific Variation in Copepods 



Studies were made of the variation in total 

 length in Caligodes laciniatus and Lernanthropus 

 belongs and in relative lengths of two setae on leg 

 5 of Parahomolochus hellones. 



As discussed under Caligodes^ the total length 

 of ovigerous females of this copepod varies widely. 

 We analyzed this variation by host and by area 

 (table 2). By area, the ranges and mean lengths 

 were : Atlantic 2.4 to 7.1 (4.36) , Indo-West Pacific 

 2.5 to 5.6 (3.70), and eastern Pacific 3.4 to 6.6 

 (4.29). By hosts, Ahlennes hians stands out with 

 by far the largest Caligodes 5.3 to 7.1 (6.03) com- 

 pared to five other host species 2.4 to 5.6 (means 

 3.77^.66). Although evidence is clear for differ- 

 ences in lengths of copepods by host species and 

 not by geographic areas; we do not know if the 

 host directly influences the growth of the copepod 

 or whether the host's enviromnent does so. 



410 



U.S. FISH AND WILDLIFE SERVICE 



