EARLY STAGES OF PINK SHRIMP FROM FLORIDA WATERS 



335 



A ventrally curved rostrum is present, on the 

 carapace. It measures from one- fourth to one- 

 third the total length of the carapace. The cara- 

 pace also bears a pair of bifurcated supraorbital 

 spines. It attains its maximum width at about the 

 level of the point of attachment of the second 

 maxillae and then gradually narrows to about half 

 that width. The posterior margin covers the an- 

 terior part, of the third thoracic somite. The 

 lateral portions of the carapace extend back 

 slightly farther than the dorsal surface. 



Gill plates are present for the first time. 



There is no great change in the structure of the 

 appendages from those of the first protozoea. A 

 single seta is added to the first antenna. Buds of 

 the thoracic appendages, the third maxillipeds, 

 and the five pairs of pereiopods appear in this 

 stage but are very rudimentary. 



The 6 thoracic and 6 abdominal segments are 

 apparent and appear very similar except for the 

 sixth abdominal segment, which is more elongate 

 than the rest. There is no line of demarcation 

 between this segment and the telson. 



Each furcal process continues to bear 7 spines. 



THIRD PROTOZOEA 



Individuals of the third protozoeal stage (fig. 

 14) measured from 2.2 to 2.7 mm. in body length, 

 based on the examination of 18 specimens taken 

 from the plankton. 



The major differences between this and the pre- 

 ceding stage are the appearance of a pair of 

 biramous uropods and of spines on the abdominal 

 somites. All of the somites are fully developed at 

 this stage. 



The carapace now covers the first five thoracic 

 somites. The small exterior spines on the supra- 

 orbital spines disappear and the latter are thus no 

 longer bifurcated. 



The 5 segments of the basal portion of the first 

 antenna are united in this stage. The second an- 

 tennae, first and second maxillae, and first and 

 second maxillipeds are essentially the same as in 

 the preceding stage. The third maxillipeds and 5 

 pairs of pereiopods liave developed further, but 

 still remain rudimentary and functionless. They 

 all are biramous. 



The abdominal somites are now considerably 

 longer than those of the thorax. The sixth ab- 

 dominal somite is about equal in length to the pre- 



ceding four combined. The sixth abdominal 

 somite is separated from the telson and differentia- 

 tion of the body somites is complete. Each of the 

 first 5 abdominal somites bears a dorsomedian spine 

 on its posterior border. In addition, the fifth 

 somite bears a pair of posterolateral spines and the 

 sixth somite bears a pair of posterolateral and a 

 pair of posteroventral spines. All of the spines 

 on the abdominal somites are directed posteriorly. 



Tlie biramous uropods are not fully developed. 

 The exopod is somewhat longer than the endopod. 

 The exopod bears 6 short terminal setae and the 

 endopod 2. 



There are now 8 spines on each furcal process, 

 with 1 having been added internally to the 7 

 already existing. 



FIRST MYSIS 



The second profound metamorphosis occurs at 

 the end of the third protozoeal stage and the larva 

 enters the first my sis stage (fig. 15). Specimens 

 in this stage measured from 2.9 to 3.4 mm., based 

 on the examination of 23 specimens taken from 

 the plankton. Tlie larva now assumes a more fa- 

 miliar shrimplike appearance. The major changes 

 are the development of the thoracic appendages 

 and the nature of the first and second antennae. 

 The carapace, uropods, and telson have also under- 

 gone extensive development. 



The carapace fits the body more closely than in 

 the protozoeal stages. The smooth rostrum does 

 not curve ventrally in as pronounced a manner as 

 in the preceding stage but projects almost straight 

 forward. There is, however, a good deal of vari- 

 ation in its form. Supraorbital spines are still 

 present, though smaller than in the protozoeal 

 stages. A spine is present at the anteroventral 

 comer of the carapace. A hepatic spine, some- 

 what removed from the anterior margin of the 

 carapace, is also present. Cephalic and thoracic 

 somites are fused in this stage. The carapace does 

 not quite cover the thorax. 



The first and second antennae have changed in 

 form as well as in function : they are no longer 

 natatory, but tactile. Tlie first antenna is divided 

 into 3 segments, the basal segment being equal in 

 length to the other 2 segments. The distal seg- 

 ment bears 2 branches, the external being twice the 

 length of the inner branch. The external branch 

 bears 6 smooth setae and the inner branch 2. 



