FISHERY BULLETIN VOL 77. NO 2 



ability in number of larval stages. Callinectes 

 sapidus, Drornidia antillensis , Rhithropanopeus 

 harrisii, Menippe mercenaria, and now M. nodi- 

 frotiK larvae have exhibited an extra instar at the 

 end of larval development iKnowlton 1974). In 

 summarizing earlier studies, Knowlton (1965, 

 1974) speculated that the amount of food, temper- 

 ature, and photoperiod contribute to controlling 

 the number of instars in decapod crustaceans. 

 Knowlton (1974) reared Palaemonetes rulgaris, a 

 caridean shrimp, under varying environmental 

 conditions and concluded that "larvae maintained 

 at increasingly higher temperature levels were 

 inclined to pass through more instars." In con- 

 trast, Sandifer (1973) found that larvae of P. vul- 

 garis "passed through fewer instars at the moder- 

 ate temperature (25°C) than at higher or lower 

 temperatures " 



Menippe nodifrons has five or (uncommonly) six 

 zoeal stages, and one megalopal stage, as does its 

 congener M. mercenaria (Porter 1960; Ong and 

 Costlow 1970). As expected (Ong and Costlow 

 1970; Costlow and Bookhout 1971; Gore 1971: 

 Christiansen and Costlow 1975) larval develop- 

 ment of A/, nodifrons was substantially slower at 

 20' C than at 30° C. The first five zoeal stages 

 exhibited modal durations ranging from 5 to 8 

 days at 20" C, 4 to 5 days at room temperature 

 (£ = 24,5° C), and 2 to 4 days at 30° C (Table 1). A 

 decrease in the number of zoeal stages was ob- 

 served concomitant with this decrease in duration 

 of each stage at the higher temperature, i.e., only 

 five zoeal stages were attained at 30° C, while an 

 atypical sixth stage was infrequently obtained at 

 both room temperature and 20° C. 



In summary, duration of larval development, 

 duration in days of each stage, and number of zoeal 

 stages of M. nodifrons, are all temperature- 

 dependent (Figure 10). Although similar results 

 were obtained by Ong and Costlow (1970) with 

 regard to larval development of M. mercenaria . a 

 difference in survival rate can be noted. At 30° C 

 none of the M . nodifrons larvae survived to crab 

 stage 1, while 30 (60% ) M. mercenaria larvae (in 

 35%n) attained crab stage 1. At similar room tem- 

 peratures (about 25° C), 1 M. nodifrons larva (27?) 

 reached crab stage 1, while 37 (74%) M. mer- 

 cenaria larvae attained crab stage 1. At 20° C, M . 

 nodifrons exhibited the highest survival with 7 

 (15%) megalopae molting to crab stage 1, while 

 survival of M. mercenaria sharply decreased to O^t 

 with no first crab stages reached ( Ong and Costlow 

 1970). 



Table 1. — Duration of larval stages of Menippe nodifrons at 

 three temperatures. 



'Zoea V moiling lo Zoea VI (penultimale). 

 ^Zoea V moiling to Megalopa (ultimate) 

 ■"Megalopa moiled Irom Zoea V 

 'Megalopa molted Irom Zoea VI 

 ( ) Died in stage 



Ong and Costlow ( 1970) suggested that 30° C is 

 the optimum survival temperature for the larvae 

 of M. mercenaria with optimum salinity ranging 

 from 30 to 35"/oii. The megalopal stage was attained 

 in 14 days, first crab on day 21, with total larval 

 survival ranging from 60 to 72% . Conversely, my 

 results indicate highest survival of M. nodifrons 

 ( 15% ) at 20° C. The megalopal stage was attained 

 in 28-34 days and first crab on days 45-49 from 

 fifth stage zoeae. Because of the additional sixth 

 stage, the megalopal stage in that series was at- 

 tained in 36-37 days and first crab on day 52. 



DISCUSSION 



Comparative Morphology oi Meni[)[)e Larvae 



The only other species of Menippe whose com- 

 plete larval development has been described is M. 

 mercenaria. Hyman ( 1925) described the prezoeal 

 and first zoeal stages of that species, and Porter 

 (1960) obtained a complete series of five (atypi- 

 cally six) zoeal stages. Menippe nodifrons also at- 

 tains five and atypically six zoeal stages, depend- 

 ing on the rearing temperature. 



There is but one easily observed and recurring 

 feature which may be used to distinguish between 

 all zoeal stages of M .nodifrons and M .mercenaria. 

 The fourth abdominal somite of M . mercenaria has 



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