EARLY STAGES OF PINK SHRIMP FROM FLORIDA "WATERS 



345 



Development of the carapace is marked by an 

 increase in size of the hepatic spines. An antero- 

 lateral spine just ventral to the eye appears in the 

 7 + 0-rostral-spine stage and increases in size at 

 each molt thereafter. 



The relative lengths of the rostrum and eye dif- 

 fer tlirongh the postlarval stages. In the first 

 postlarval stage, the rostrum extends to the edge 

 of the eye or exceeds it in length when the eye is 

 extended forward. The rostrum becomes short- 

 ened in the second jx)st]arval stage to aliout two- 

 tliirds the length of the eye, and does not again 

 equal it in length until ai)proximately the 8 + 2- 

 rostral-spine stage is reached. Thereafter, the 

 rostrum is somewhat longer than the extended eye. 



DISCUSSION 



The number of stages in each of the phases 

 through which the larvae pass has been found to 

 vaiT with the species. Hudinaga (1942) reared 



PiGUKE 20. — Carapace and rostrum in advanced post- 

 larvae. (A) 6.9mm. (B) 7.2mm. (C) 9.0mm. (D) 

 10.2 mm. (E) 9.3 mm. (F) 10.4 mm. (G) 11.1 mm. 

 (H) 12.6 mm. (I) 13.5 mm. (J) 15.5 mm. (K) 15.5 

 mm. (L) 17.8 mm. (M) 18.6 mm. 



the larvae of P. japonicus through 6 nauplial 

 stages, while Heldt (1938) found 8 in P. trimlca- 

 tus. Peai-son (1939) found 5 nauplial stages in 

 P. setifer'us, while Heegaard (1953), working only 

 with planktonic material, found 3 stages for the 

 same species. All of these authors found that the 

 species with which they were working passed 

 through 3 protozoeal stages, while 3 mysis stages 

 were observed in P. japonicus, 4 in P. trmthatus, 

 and 2 in P. -sefiferi/.s. Broad ( 1957) noted a varia- 

 tion in the number of lan'al stages in Palaemone- 

 tes, depending on the quantity of food available. 



COMPARISON WITH P. SETIFERUS 



The number of nauplial stages found in this 

 study for P. diwrarmn was five, the same as was 

 foiuid by Pearson for P. setiferus, but there are 

 slight differences between the corresponding stages 

 of the two species. In the firet nauplius, Pearson 

 made no mention of the dorsomedian spine near 

 the posterior end of the body that was noted in 

 P. duorarwri: Pearson found the second nauplius 

 of P. setifems possessed two pairs of furcal spines. 

 Heegaard described as a first nauplius of the same 

 species a stage which the editors of his paper con- 

 cluded was a second nauplius because of the 

 appearance of setules on its setae. This stage 

 had a single pair of furcal spines, the condition 

 found in the second nauplius of P. duorarwn. 

 Pearson found frontal organs on the fourth and 

 fifth nauplial stages, while Heegaard found them 

 on his "last" nauplial stage and first protozoea. 

 Frontal organs were seen only on the fifth nauplius 

 of P. duorarwm; however, they may also be present 

 on the fourth nauplius. 



Of considerable interest is the number of mysis 

 stages. Pearson describes two mj'sis stages and 

 Heegaard does likewise. An editorial iiot« in 

 Heegaard's paper states, "Heegaard's 'Second 

 Mysis' appears to represent a considerably less 

 advanced stage than Peareon's and it seems prob- 

 able that there are more than two mysis molts in 

 P. setifems (of. Heldt, 1938, and Hudinaga, 1942, 

 on other species of Penaeus) ." This appears true 

 for certain characters, e.g., the absence, of a rostral 

 spine, but other structures, such as the telson, ap- 

 jiear to be well developed. 



Three mysis stages were found in the develop- 

 ment of P. diioramm. The presence of three 

 stages was based upon the development of the 



