NO- 3582 GENUS ENTOMACRODUS — SPRESTGER 111 



other member of the nigricans group occurs). 



Some of the specimens of E. chiostictus from Clipperton and Clarion 

 Islands appear to be intermediate between E. sealei and E. caudofasci- 

 atus and can be expected to key to either of these two western Pacific 

 species, especially to the Rarotonga, Tahiti, Makatea, and Raroia 

 populations of E. caiidqfasciatus (these populations represent the east- 

 ernmost occuiTences of E. candojasciatns; the easternmost occurrence 

 of E. sealei is Raroia). E. chiostictus, in common with E. sealei and 

 E. caudofasciatus, has a proportionately longer supraorbital cirrus 

 than is found in the Atlantic members of the nigricans species group. 

 This fact and the increased occurrence of paired pores in the pre- 

 opercidar series of pores of E. chiostictus over their occiu-rence in the 

 Atlantic species (and E. caudojasciatus) appears to relate E. chiostictus 

 most closely with E. sealei. It would seem, therefore, that at some 

 time individuals of the form ancestral to E. sealei and E. chiostictus 

 reached eastern Pacific shores and diverged. Differentiation appears 

 to be more advanced in the mamland populations than in the Clarion 

 Island and Clipperton Island populations. 



Support for an Indo-West Pacific origin of the species ancestral to 

 E. chiostictus is the appearance in the eastern Pacific (but not the 

 western or eastern Atlantic) of a blenniid genvis, Runula, which has 

 the Indo-West Pacific as its center of abundance. Other blennioids, 

 certain Tripterygiidae (R. H. Rosenblatt, pers. comm.), subfamily 

 Clininae, of the Clinidae (M. L. Penrith, in litt.), found in the 

 eastern Pacific also have their closest relatives in the western Pacific 

 and no closely related representatives in the Atlantic. Briggs 

 (1961) has postulated a western Pacific origin of all the shore fishes 

 not worldwide in distribution and foimd common to both the eastern 

 and western Pacific ocean. He bases this on the direction of flow 

 of ocean currents, the fact that most of the genera in common have 

 far more species in the western Pacific than in the eastern Pacific, 

 the fact that most of the forms occur primarily or only on the off- 

 shore islands in the eastern Pacific, and the fact that no species of a 

 typically tropical New World genus has colonized the western Pacific. 

 The evidence, though circumstantial, thus also favors an Indo-West 

 Pacific origin of the form ancestral to Entomacrodus chiostictus. 



I believe that Entomacrodus reached the eastern Pacific by island 

 hopping and by movement of populations along rocky coasts. The 

 most probable route would be along the chain of islands extending 

 out to Easter Island and Sala-y-Gomez, thence along formerly exist- 

 ing islands of the Sala-y-Gomez and Nasca Ridges to Peru, and up 

 the coast to Central America and Mexico. The movement would 

 have taken place during a period of warmer climatic conditions than 

 exist today. Subsequent climatic cooling would have eliminated the 



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