KNIGHT: STAGES OF THYSASOPODA TRICUSPIDATA 



in many respects. The partial segmentation of 

 antennal exopod in the nauplius II and the form 

 and armature of carapace and telson of the meta- 

 nauplius may be distinctive, the rudimentary 

 setation of mouthparts in calyptopis I appears 

 to be unusual — indeed the larva seems ill- 

 equipped to feed, there seems to be a reduction 

 in dentition of mandibles and in numbers of setae 

 on mouthparts in calyptopes II and III, and the 

 carapace of calyptopis III is transitional between 

 the usual calyptopis and furcilia forms. In ad- 

 dition, the larvae are known to deviate from 

 trends within the genus in development of ab- 

 dominal pleopods during the furcilia phase. Ac- 

 cording to Lebour (1950), T. tricuspidata is the 

 most variable in pleopod succession of any 

 Thysanopoda species, indeed of any euphausiid 

 known and, as it has been demonstrated that 

 there is a correlation between a more rigidly de- 

 fined number of furciliar stages and a more 

 oceanic distribution within the genus Thysan- 

 opoda (Mauchline and Fisher, 1969), such var- 

 iability in the oceanic species T. tricuspidata is 

 surprising. 



Although there is too little information avail- 

 able at this time for speculation as to the sig- 

 nificance of the unusual morphological features 

 observed in this study, the details found in the 

 literature did support the identification of the 

 larvae in that the combination of setation of 

 endopod and exopod of the maxillule and endopod 

 of the maxilla of T. tricuspidata calyptopes was 

 not noted or figured in descriptions of the larvae 

 either of other species of Thysanopoda or of 

 other genera of the family. 



ACKNOWLEDGMENTS 



I wish to thank E. Brinton for his assistance 

 and criticism of the manuscript, and we both 

 wish it to be known that the plankton sorting 

 staff at the Indian Ocean Biological Centre first 

 identified the unique metanauplius as a euphau- 

 siid. 



This work was supported by the Marine Life 

 Research Program, the Scripps Institution of 



Oceanography's component of the California 

 Cooperative Oceanic Fisheries Investigations, 

 a project sponsored by the Marine Research 

 Committee of the State of California, and by 

 the Oceanography Section, National Science 

 Foundation, NSF Grant GA-31783. 



LITERATURE CITED 



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In press. The distribution of Indian Ocean euphau- 

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 EiNARSSON, H. 



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1939. Larval stages of the euphausiid Thysanopoda 

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 Gopalakrishnan, K. 



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1885. Report on the Schizopoda collected by H. M. 

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