THE NAUPLIUS II, METANAUPLIUS, AND CALYPTOPIS STAGES OF 

 THYSANOPODA TRICUSPID AT A MILNE-EDWARDS (EUPHAUSIACEAJ 



Margaret D. Knight' 



ABSTRACT 



A large, spinose metanauplius, a nauplius II, and calyptopis I, found in the Indian Ocean 

 and Equatorial Pacific, are referred to Thysanopoda triciispidata. The identifications 

 are based on the distinctive morpholog-ical features shared by these larval stages and by 

 the calyptopes II and III of T. tricuspidata identified by Sars (1885), and on the observed 

 distribution of T. tricuspidata and the metanauplius in the Indian Ocean. Calyptopes 

 II and III are redescribed to present the complete calyptopis phase of larval development 

 in one account. 



During a survey of euphausiids in the Indian 

 Ocean (Brinton and Gopalakrishnan, in press), 

 many specimens of a relatively large and very 

 ornate metanauplius were found. There was 

 conjecture that the curious, apparently unde- 

 scribed form might be the larva of a species of 

 the genus Thysanopoda, and it was sought for 

 next in plankton from the Equatorial Pacific. 



The metanauplius was found in these waters 

 as were specimens of a seemingly related nau- 

 plius II and calyptopis I together with the calyp- 

 topis II, calyptopis III, furcilia, and juvenile 

 stages 0/ Thysanopoda tricuspidata identified by 

 Sars (1885). When individuals of each of the 

 larval stages were placed together, they appeared 

 to form a natural developmental series; their 

 relative size, the distinctive shape of developing 

 eyes, telson, and carapace all suggested that the 

 larvae were progressive stages of the same spe- 

 cies. Evidence of their specific relationship was 

 found in a detailed study of these features and 

 of the morphology of larval appendages, and 

 there seemed to be sufficient justification for re- 

 ferral of the three unidentified early stages to 

 T, tricuspidata. 



Redescriptions of the calyptopes II and III of 

 T. tricuspidata are included in this paper with 



' Scripps Institution of Oceanography, University of 

 California at San Diego, La JoUa, CA 92038. 



Manuscript accepted June 1972. 



FISHERY BULLETIN: VOL. 71, NO. 1, 1973. 



identification and description of the nauplius II, 

 metanauplius, and calyptopis I, in order to pre- 

 sent the complete calyptopis phase of the spe- 

 cies in one account and to illustrate the setation 

 of appendages more fully. 



METHODS AND MATERIALS 



Specimens of the metanauplius were observed 

 in the standard collections, approximately 

 200-0 m depth, obtained during the International 

 Indian Ocean Expedition (IIOE), 1962-65. 

 About 100 metanauplii were removed for study. 

 The distributions of T. tricuspidata and the 

 metanauplius based on the data of Brinton and 

 Gopalakrishnan are shown in Figure 9. 



Selected samples taken during EQUAPAC 

 Expedition by RV Stranger of the Scripps In- 

 stitution of Oceanography in August-September 

 1956 between long 165°-175°W and lat 6°S-10°N 

 by oblique tow in the top 200 m (Snyder and 

 Fleminger, 1965) were sorted for the metanaup- 

 lius and calyptopes. Positions of the samples 

 yielding larvae and the developmental stages 

 found in each sample are given in Table 1. The 

 distribution of T. tricuspidata in the Pacific is 

 described by Brinton (1962). 



For measurement with an ocular micrometer, 

 the larvae were straightened in a few drops of 



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