COOK and MURPHV: DEVELOPMENTAL STAGES OF BROWN SHRLVIP 



POSTLARVA I 



(Fig. 13) 

 Mean TL = 4.6 mm (4.2-5.0 mm) 

 Mean CL = 1.5 mm (1.4-1.6 mm) 



N = 15 



No drastic changes in morphology are as- 

 sociated with the molt from the third mysis 

 to the first postlarval stage. The pleopods, now 

 well developed and setose, are the principal 

 swimming organs. There is usually a reduction 

 in the size of the exopods of the pereiopods, 

 which, if present, are only vestigial. 



The carapace is much the same as in the third 

 mysis. The rostrum bears one or two spines and 

 extends slightly beyond the distal border of the 

 eye. The small spine present on the antero- 

 ventral corners of the carapace in the preceding 

 substage is absent. The supraoi'bital spines are 

 now minute or absent. A pair of hepatic spines 

 and ocelli are present. 



The inner branch of the first antenna is com- 

 posed of two segments, and the outer, three. 

 The statocyst at the base of the first antenna 

 is fully developed. The endopod of the second 

 antenna is composed of five or six frequently in- 

 distinct segments. The exopod bears 23 setae. 



The mandibular palp is two-segmented and 

 possesses five setae. 



The endopods of the first and second maxillae 

 have been reduced greatly and are now unseg- 

 mented and usually without setae. Setation of 

 the protopod of the second maxilla has been re- 

 duced while its exopod has become enlarged and 

 now bears 21 setae. 



The first maxilliped retains only rudiments 

 of its endopod and exopod. The second and third 

 maxillipeds and the first pereiopod have lost all 

 but a vestige of their exopods. The endopod 

 of the second maxilliped has become recurved, 

 and its setation has changed greatly: the first 

 segment has three setae; the second, four; the 

 third, one; the fourth, five; and the fifth, six. 

 The second and third segments of the endopod 

 of the third maxilliped have each gained one 

 seta, the fourth, three; the number of setae on 

 the terminal segment varies from three to six. 

 The dactyl of the first pereiopod now possesses 

 several small teeth and short bristles terminally. 



Each pleopod is composed of two segments, 

 the distal one bearing about 10 setae. 



The presence of dorsomedian spines on the 

 third, fourth, and fifth abdominal segments is 

 variable. Such spines may be absent or present 

 on one or more of the segments. The midlateral 

 spines have been lost from the fifth and sixth 

 segments. The sixth segTnent retains a dorso- 

 median and paired ventrolateral spines. 



The telson, which is now only faintly cleft, 

 bears five pairs of terminal and three pairs of 

 lateral spines. 



COMPARISON WITH 

 PINK AND WHITE SHRIMP 



During the fall of 1964, pink shrimp hatched 

 from eggs spawned in the laboratory were 

 reared to postlarvae. White shrimp were reared 

 during the summer of 1966. Examination of 

 these larvae showed them to be identical to 

 brown shrimp larvae in setation and other ma- 

 jor morphological characteristics. Various parts 

 of the body were measured to determine if body 

 proportions differed between the species; the 

 results proved inconclusive. 



Dobkin (1961) described the larval develop- 

 ment of the pink shrimp but was absolutely 

 certain only of the identity of the nauplial and 

 first protozoeal substages which he obtained 

 from eggs hatched in the laboratory. Descrip- 

 tions of the more advanced stages were based 

 on specimens sorted from plankton samples. 

 When the pink shrimp we had reared were com- 

 pared with the specimens described by Dobkin, 

 several diflferences were noted. These are listed 

 in Table 1. 



Pearson (1939) and Heegaard (1953) de- 

 scribed the larval development of the white 

 shrimp from material taken in plankton tows. 

 Com]3arison of these descriptions and our spec- 

 imens was not attempted because we feel both 

 Pearson's and Heegaard's descriptions of the 

 later stages are not detailed enough for itemized 

 comimrison. In addition, Heegaard's editors felt 

 that his figures of the first and second protozoeae 

 were not referable to P. setiferus, but should be 

 attributed to Trachypenaeus, Sicyonia, or Xlph- 

 openaeus. From material at our disposal it 



237 



