THE GENUS CHORISMUS 



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DISCUSSION 



This species provides an interesting example of abbreviated development. In 

 Bythocaris and Cryptocheles the free larva is entirely suppressed (Sars, 1885), the young 

 hatching in the form of the adult. In Spirontocaris polaris the first free larva is much 

 more developed than in Chorismus antarcticus and has lost all the characters distinctive 

 of stage I (Stephensen, 1935). 



In Chorismus the first larva, though it has the full number of appendages, retains 

 certain characters of the normal first larva which one would think might well have been 

 lost. For example the antennule is unsegmented and has no trace of the inner branch; 

 the antennal scale has no spine, and retains traces of segmentation and few setae, while 

 the flagellum, though so far developed, terminates in a denticulate spine, showing that 

 it has developed from the spine-like form found in Hippolyte and Spirontocaris but not 

 in Caridion. The exopods, although furnished with far more setae than is normal in 

 stage I, have the apical setae arranged asymmetrically, as is usual in stage I in Hippo- 

 lytidae and certain genera of other families of Caridea. 



When development is shortened it is commonly the case that the telson has more 

 than the normal number of spines (e.g. Sabinea, Palaemon boreUii). Sollaud (1923) has 

 already noted the retention of some of the characters of the normal stage I in Palaemo- 

 nidae in which larval development is greatly shortened or suppressed, and particularly 

 that the telson retains the wide triangular form until transformation to the adult. 



Distribution of larvae of Chorismus antarcticus 



