EARLY STAGES OF PINK SHRIMP FROM FLORIDA WATERS 



329 



FOURTH NAUPLIUS 



The fourth nauplii (fig. 8) examined measured 

 from 0.48 to 0.55 mm. in body length and from 

 0.18 to 0.20 mm. in greatest body width. Six speci- 

 mens that had been reared from eggs were studied. 

 The major differences between tliis and the pre- 

 ceding stage are in tlie number of furcal spines, 

 the appearance of tlie next four pairs of appen- 

 dages, and segmentation and setation of the 

 appendages. 



Tliere are now 5 spines on each furcal process, 

 with the addition of 2 weak sjjines external to the 



3 already present in the preceding stage. The 

 longest spine bears minute barbs, while the other 



4 are smooth. 



This stage is the first in wliich there is a definite 

 segmentation of the appendages. This segmenta- 

 tion is often indistinct and the best criterion for 

 its determination is the presence of indentations 

 along the margins of the appendages. 



The frontal organs reported to be present in late 

 nauplial stages in several other species of penaeids 



were never seen in this stage in P. dxMrarwm, al- 

 though several specimens were examined under 

 500 power specifically for this character. 



FIFTH NAUPLIUS 



Individuals of the fifth nauplial stage (figs. 9 

 and 10) measured from 0.53 to 0.61 mm. in body 

 length and from 0.17 to 0.20 mm. in greatest body 

 width, based on 28 specimens raised from eggs. 

 The most noticeable differences between this and 

 the preceding stage are the development of the 

 masticatory portion of the mandible, the trans- 

 parency of the endopod of that appendage, the in- 

 creased number of furcal spines, the outline of a 

 future carapace, and the setation of the 

 appendages. 



The furcal processes now bear 7 spines each, 

 with the addition of 2 spines, 1 weak and 1 mod- 

 erate, internal to the 5 found on each furca in the 

 preceding stage. The 3 median spines bear minute 

 barbs. 



Frontal organs were observed on the anterior 

 margin of several fifth nauplii taken from the 



FiGUBE 8. — Ventral view of fourth nauplius. 



