FISHERY BULLETIN: VOL. 77, NO, 2 



Table 4. — Taxonomically important characters of the fifth zoeal stage in two species otMenippe. 



ditions, are distinguished from other xanthid gen- 

 era by attaining five and atypically six zoeal 

 stages; other xanthid larvae exhibit only four 

 zoeal stages. Larvae of the genus Menippe (and 

 Eriphia ) are distinguished from other xanthids by 

 antennal development, i.e., the larval exopodite is 

 about 0,75  the length of the spinous protopodal 

 process (see Aikawa 1937; Porter 1960; Sandifer 

 1974), Menippe (and Sphaerozius) larvae are dis- 

 tinguished from other closely related xanthid gen- 

 era by the absence of setae on the basal segment of 

 the second maxillipedal endopodite (Aikawa 1937; 

 Porter 1960), 



Number of Zoeal Stages 



According to descriptions to date, every genus of 

 xanthid crab has four zoeal stages ey^cept Menippe. 

 In this study, M. nodifrons attained five zoeal 

 stages, occasionally a sixth, and a prezoeal stage 

 occurred. These stages also appeared in the larval 

 development of A/, mercenaria (Porter 1960). The 

 prezoeal stage exhibited by both M. mercenaria 



and M. nodifrons was never observed to molt to a 

 first stage zoea. Larvae of both species, collected 

 within seconds after hatching, were almost always 

 found to be in the first stage, indieatmg that the 

 observed M . nodifrons prezoeae were those zoeae 

 too weak to molt to stage L Porter also indicated 

 that M. mercenaria prezoeae. which were seen 

 most often when subsequent survival was poor, 

 may not be a normal stage in planktonic existence 

 of the larvae. However, Lebour (1928), Chamber- 

 lain (1957), and Wear (1970) established that lar- 

 vae of other xanthid genera hatch from the egg as 

 prezoeae. Based on data obtained in this experi- 

 ment, it seems possible that the prezoeal stage of 

 M. nodifrons may occur in nature under certain 

 conditions, as may the sixth zoeal stage. 



Porter ( 1960) suggested that, based on the var- 

 iability of morphological characters and the fact 

 that no stage VI zoeae molted to megalopae. the 

 sixth stage in M. mercenaria may not be a true 

 stage but an advanced fifth stage. As noted in the 

 rearing results, the observation of temperature- 

 dependency in relation to number of zoeal stages 



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