NO. 3582 GENUS ENTOMACRODUS — SPRINGER 113 



see Sachet, 1962, p. 25; for diagrams of the current, see Wyrtki, 1965). 

 Clipperton Island, closest tropical eastern Pacific island to the tropica] 

 central Pacific atolls, is 2300 miles from the nearest such atoll, 

 the Tuamotus; however, the Tuamotus lie in the path of the South 

 Equatorial Current and would not be expected to contribute faunal 

 elements to the eastern Pacific. The Line Islands, over 4000 nautical 

 miles from Clipperton, are the nearest central Pacific atolls to Clipper- 

 ton lying in the path of the Equatorial Coimtercurrent. Movement 

 of this current is about 0.75 knot per hour (Wyrtki, 1965). At this 

 speed it would require well over 200 days for an individual larva to 

 travel from the Line Islands to Clipperton. It seems unlikely that 

 Entomacrodus larvae would be the forms transported, as it appears 

 from the small size at transformation (less than 25 mm SL) that En- 

 tomacrodus species have only a brief larval life. 



It is also difficult to postulate adult transport (for instance bj^ 

 flotsam). The problem here is that adults are bottom dwellers found 

 only in rocky or coral reef areas; no adidts have been recorded from 

 the open ocean out of sight of land or from near floating objects. 



Assuming that Entomacrodus did reach the eastern Pacific from the 

 western Pacific, it seems probable that the genus moved from the 

 eastern Pacific to the western Atlantic during times when there was 

 a Central American passage between the eastern Pacific and the west- 

 ern Atlantic. When the isolating Central American land bridge ap- 

 peared, the populations on either side diverged. (It seems probable, 

 however, that the eastern Pacific population did not diverge from the 

 central Pacific population until well after the isolation of the Pacific 

 from the Atlantic, and therefore the Atlantic populations are more 

 divergent from the ancestral form than are the eastern Pacific popula- 

 tions.) Subsequently, the western Atlantic form populated other 

 areas of the Atlantic, and these populations in turn diverged. The 

 progressively lower percentage of specimens with paired pores occur- 

 ring in the preopercular series of pores as one examines populations 

 from the central Pacific (E. sealei and E. corneliae), eastern Pacific 

 {E. chiostictus), western Atlantic (E. nigricans, E. vomerinus), and 

 eastern Atlantic {E. cadenati, E. textilis), would support this reasoning. 

 In this scheme E. caudofasciatus, with predominantly simple pores, 

 presents the only problem. Its distribution, eastern Indian Ocean 

 to the Tuamotus, and the fact that there are several differentiated 

 populations as opposed to the undifferentiated populations of E. sealei, 

 seems to indicate a species of limited mobility whicli originated in the 

 Indo-West Pacific area and has remained there. Confusing specimens 

 of E. chiostictus would then represent convergent rather than direct 

 relationship with E. caudojasciatus (and E. sealei). 



