Survival, duration of intermoult cycle and respiratory metabolism were evaluated as a function of salinity (0-35%0 ; 25 ° C) in early zoeae of the cinnamon shrimp, Macrobrachium amazonicum . Zoeae are extremely resistant to salinity, mortality occurring only in fresh and sea-water after several days . Moulting occurs in all salinities, longer cycles being recorded in 0 and 35% 0 S . The metabolism-salinity curve is broadly U-shaped between 0 and 28% 0 S but declines sharply in sea-water. Such physiological responses characterise the early zoeae as strongly euryhaline and typically estuarine . Data are discussed in relation to the degree of adaptation of the organism to the freshwater biotope and the position of the species within the generic pattern of adaptive radiation .
This paper reports the species of Macrochiridothea occurring up to now on the continental shelf of southern Brazil. Two species are new to science: M. marcusi sp. n. and M. lilianae sp. n.. M. stebbingi Ohlin, 1901, is the third species reported for the area. The genus now comprises 8 species. A diagnosis for the genus, as well as for alI the species is given, together with comprehensive illustrations to permit prompt recognition of the species. Secondary sexual dimorphism is reported for the first time in the genus. A elassification key based on adults is furnished, and remarks or eomments for eaeh speeies are made. The geographie range for the genus has been considerably extended to the north, to about Lat. 23º07'S. General ecological and zoogeographieal remarks are made.
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