EARLY STAGES OF PINX SHRIMP FROM FLORIDA "WATERS 



343 



The first 3 pairs of pereiopods consist of a pe- 

 duncle of 2 segments and an endopod of 5. Tlie 

 chela is formed by the fourth and fifth segments 

 of the endopod. Tlie fourth and fifth pereiopods 

 have the same number of segments as the first three 

 but do not bear chelae. Instead, the fifth segment 

 of the endopod is slightly cur\'ed and pointed. 



The pleopods have 3 segments, the most distal 

 of which bears about 10 setae. The first three 

 pleopods are better developed than the fourth and 

 fifth. 



The dorsal abdominal spines are variable in this 

 stage. Almost all specimens examined had a dor- 

 sal spine on tlie fifth segment. Some had small 

 spines on the third and fourth segments, but others 

 did not. The dorsal spine on the third abdominal 

 segment was the one most often missing. The 

 lateral spines on the fifth abdominal segment were 

 absent on almost all first postlarvae examined, but 

 were present, although reduced, on at least 1 speci- 

 men. The 2 paire of lateral spines on the sixth 

 abdominal segment have disappeared. 



The telson is further elongated and now bears 

 3 pairs of lateral and 5 pairs of terminal spines. 

 The notch is further reduced, its tip falling be- 

 tween the most posterior pair of lateral spines and 

 the terminal spines. 



SECOND POSTLARVA 



Individuals of the second postlarval stage (fig. 

 19) measured from 4.7 to 6.6 mm., based on 22 

 specimens taken from the plankton. 



The chief difference between this stage and the 

 first postlarval stage is the presence of a second 

 dorsal spine on the rostrum. In addition, the ros- 

 trum is shortened and does not reach the end of the 

 eye when the latter is extended forward. 



The inner of the 2 branches from the distal end 

 of the first antenna is now somewhat longer than 

 the external branch and has 3 segments. The 

 flagellum of the second antenna is larger and is 

 composed of 5 segments. 



The maxillae are more developed. The sca- 

 pliognathite of the second maxilla is larger and 

 l)e.ars approximately 30 setae. 



The endopod of the first maxilliped is much 

 smaller than the exopod, and the mastigobranchial 

 plate has developed greatly. The second maxilli- 

 {ie<l is curved to a gi-eater degree than in the first 



jxtstlarva, while the third maxilliped is essentially 

 the same. The same is true of the pereiopods and 

 pleopods. 



There are no spines on the third through fifth 

 abdominal segments. 



The telson does not differ markedly from the 

 l)receding stage. The notch, however, is some- 

 what less evident. 



ADVANCED POSTLARVAE 



A series of specimens of postlai"vae (fig. 20) 

 from the 3-dorsal rostral-spine stage through the 

 10-dorsal and 2-ventral rostral-spine stage, meas- 

 uring from 5.7 to 18.6 mm., was examined (see 

 table 2). From the work of Hudinaga (1942) 

 on P. japonien.s, it appears probable that several 

 molts occur, with the postlarvae retaining the same 

 number of rostral spines. Hudinaga's observa- 

 tions were made on living material. Although the 

 present study dealt exclusively with preser\-ed ma- 

 terial, it was noted that the anteriomiost rostral 

 spine of a group of postlarvae having the same 

 number of rostral spines often varied in size. 

 Since this spine is always the one most recently 

 developed, this may be added proof for the sup- 

 position that the same number of rostral spines 

 are retained through several molts. 



The first ventral spine on the rostrum appears 

 in the stage that has 7 dorsal rostral spines (at 

 approximately 10 to 11 mm.), although the stage 

 or stages preceding it have 7 dorsal and no ventral 

 rostral spines. Likewise, the second ventral spine 

 appears when 8 dorsal spines are present (at ap- 

 proximately 12.5 to 13.5 mm.), although there are 

 specimens with 8-1-1 rostral spines. 



The biramous condition of the pleopods is first 

 clearly evident in the 8 + 1 stage, but development 

 may have begun in the preceding stage. 



Table 2.— Measurements of 48 advanced-stage postlarvae 

 examined 



' Adult P. duorarum have 9 or 10 rostral spines. 



