FLEMINGER: INTEGUMENTAL ORGANS IN GENUS EUCALANUS 



species but one pair being sufficiently distinctive 

 in number and arrangement to be identifiable 

 solely on the basis of integumental organs. 

 Species grouped on the basis of integumental 

 organs concur with groupings that utilize the 

 seminal receptacle, segmentation of the abdo- 

 men and structure of the male fifth legs. In 

 general, variation was negligible; about 80% of 

 the sites in each species was observed in all 

 specimens examined and an additional 10% ap- 

 peared in from 80 to 99% of the specimens. The 

 mean number of organs observed in samples 

 of each population ranged from a low of 83 to a 

 high of 135 in a combined total of 448 randomly 

 selected specimens representing the 17 species 

 in the genus. 



5. Comparison of geographical relationships 

 and number of integumental organs within 

 each species group indicates that the species 

 with the broadest geographical range is also the 

 one with the most distinctive number or ar- 

 rangement of integumental organs especial- 

 ly with respect to organs on the genital seg- 

 ment. The combination of species specificity, 

 phylogenetic relationships, and geographical 

 patterns associated with numbers and ar- 

 rangement of organs indicate that the organs 

 may function in prezygotic mating barriers 

 within the genus. 



6. Comparison of total length and number of 

 integumental organs indicates that the two 

 features are unrelated. 



7. Variation in integumental organs in the 

 circumglobal broadly tropical species E. subte- 

 Huis was found to have a strong geographical 

 pattern indicating limited gene flow between 

 the populations of the Eastern Tropical Pacific, 

 the Indo-West Pacific, and the Atlantic Ocean. 

 Some sets of organs were found to vary inde- 

 pendently; others appeared to vary similarly 

 providing evidence that the genetic control is 

 complex. Their responses to selection pressures 

 appear to vary sufficiently to warrant detailed 

 study of subtonds in relation to its closest 

 cognate, inucronatu.s, within and outside of 

 their region of co-occurrence. 



8. Limited examination of males and cope- 

 l)odid stages III to V indicate that the integu- 

 mental organs appear in the same numbers and 

 arrangements that characterize the adult female 



except for structures that have not yet com- 

 pleted sexual maturation or are sexually dimor- 

 phic. 



9. The attenuatus complex is revised on the 

 basis of integumental organs and geographical 

 distribution. Four biologically discrete popula- 

 tions are recognized, three being described as 

 new species. 



ACKNOWLEDGMENTS 



This research was supported by National 

 Science Foundation Grants (GB 12412, GA 

 31092, GB 32076) and by the Marine Life Re- 

 search Group of Scripps Institution of Oceano- 

 graphy. I am particularly grateful to my two 

 colleagues: K. Hulsemann whose meticulous 

 editing and compilation of the manuscript 

 significantly improved its accuracy and expe- 

 dited its completion and J. Behrhorst who car- 

 ried out scanning electron microscopy and pre- 

 pared Figure 2. 



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