COOK anJ MLRPHY: DEVELOPMENTAL STAGES OF BROWN SHRIMP 



have two setae, and the fourth, three. The ex- 

 opod has five setae. 



The first maxilliped is biramous and longer 

 than the maxillae. It has a protopod of two 

 segTnents, an endopod of four segments, and an 

 unsegmented exopod. The protopod bears about 

 17 setae. The basal segment of the endopod 

 possesses three setae; the second, one or two; 

 the third, two; and the terminal, five. The 

 exopod has four lateral and three terminal setae. 



The second maxilliped, though smaller, is al- 

 most identical to the first. The protopod bears 

 six setae. The endopod is composed of four seg- 

 ments, the first and third giving rise to two 

 setae; the second, one or two; the fourth, five. 

 The exopod has three lateral and three terminal 

 setae. 



The third maxilliped is present only as a small 

 bud. 



The caudal furcae each retain seven spines 

 and are separated by a well-defined anal opening. 

 The digestive tract is visible posterior to the 

 labrum. 



The body is colorless and almost transparent 

 with the exception of two red spots, one on each 

 side of the anal opening. 



PROTOZOEA II 



(Fig. 8) 

 Mean TL = 1.71 mm (1.28-2.01 mm) 

 Mean CL = 0.80 mm (0.72-0.87 mm) 



N = 25 



The most apparent modification from the pre- 

 ceding substage is the presence of stalked com- 

 pound eyes. Additional features that charac- 

 terize this substage are a ventrally projecting 

 rostrum, a pair of bifurcate supraorbital spines, 

 and a segmented abdomen. 



Frontal organs are absent in this and later 

 stages. 



Segmentation of the appendages remains the 

 same as described for the first protozoea. The 

 only changes in setation are on the first antenna. 

 Several setules are added near the posterolateral 

 seta on the second segment, and an additional 

 terminal seta is found on the last segment. Ru- 

 diments of the third maxilliped and five pairs 

 of pereiopods are present. 



The abdomen is divided into six segments, the 

 telson not being separated from the sixth. The 

 number of furcal spines remains constant at 

 seven pairs. 



PROTOZOEA III 



(Fig. 9) 

 Mean TL = 2.59 mm (2.40-2.59 mm) 

 Mean CL = 1.06 mm (0.93-1.40 mm) 



N = 15 



The principal diflferences between this sub- 

 stage and the preceding one are the presence 

 of biramous uropods and spines on the abdom- 

 inal segments. 



The carapace is close fitting and covers all 

 but the last three thoracic somites. The supra- 

 orbital spines are no longer bifurcate. 



The five subsegments comprising the basal 

 section of the first antenna in the preceding 

 protozoeal substages have fused into a single 

 unit. The ventrolateral seta that originated 

 from the middle of the second segment has been 

 lost, and a similar one is present on the distal 

 margin. The second antenna, mandible, and 

 maxillae remain essentially the same as in the 

 preceding substage. Two setae have been added 

 to the exopod of the first maxilliped. The first 

 segment of the endopod and the exopod of the 

 second maxilliped have gained a seta. Although 

 the third maxilliped and five pereiopods have 

 developed further and are now biramous, they 

 remain functionless. 



The abdomen is divided into six segments, the 

 telson being distinct from the sixth segment. 

 The sixth segment is about three-fourths the 

 length of the preceding five combined. Each 

 of the first five segments has a dorsomedian 

 spine on its posterior margin. The fifth seg- 

 ment also possesses a pair of midlateral spines, 

 and the sixth somite has paired midlateral and 

 ventrolateral spines. 



A pair of biramous uropods are present, orig- 

 inating from the ventroanterior mai'gin of the 

 telson. The exopod, slightly longer than the 

 endopod, bears five or six setae at its apex. 



An additional pair of caudal spines have been 

 added medially on the telson, making a total of 

 eight pairs. 



229 



