FISHERY BULLETIN: VOL. 73, NO. 3 



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It seems noteworthy that P. vannamei is the 

 only species of the subgenus Litopenaeus in which 

 a strongly developed median protuberance 

 (projecting from sternite XIII) is present on the 

 thelycum. Females of the remaining species of 

 Litopenaeus lack a median protuberance, unlike all 

 of the other species of Penaeus. In the former 

 females, the midposterior part of sternite XIII 

 bears instead a simple, relatively small knob-in P. 

 occidentalis— or is produced into a shelf which 

 overhangs sternite XIII. This shelf is horizontal in 

 P. schmitti and P. setiferus, and subvertical in P. 

 stylirostris. 



The spermatophore of P. occidentalis is con- 

 siderably more elaborate than that of P. van- 

 namei, although the sac is structurally similar in 

 the two and simpler than that of P. stylirostris. 

 The spermatophore of P. occidentalis, unlike that 

 of P. vannamei, possesses a wing and, unlike all 

 other species of Litopenaeus, bears an anterior 

 lobe, and is produced caudally in a very short 

 flange. Also, it bears the largest lateral blade to be 

 found in any of them, the blade being divided in 

 several sections and continuous with the typical 

 stiffened ventromesial extension, ending in a 

 rather flexible caudal lobe; that extension seems to 

 correspond to the flap borne by spermatophores of 

 the other species. In addition, the spermatophore 

 of P. occidentalis possesses a unique transverse 

 lamina on the anterior extremity of the sac, which 

 is not intimately associated or even firmly at- 

 tached to it or to the other contiguous components, 

 i.e., the anterior lobe and the wing. In this sper- 

 matophore, however, the flange is inconspicuous, 

 consisting of a short rigid shelf at the posterior 

 end of the sac. Finally, the compound sperma- 

 tophore of P. occidentalis is affixed to the female 

 farther anteriorly than in the other species, the 

 anterior lobes extending over (ventrally) the coxae 

 of the third pereopods to become attached to ster- 

 nite XII; this brings the openings of the sacs to the 

 scooplike coxal plates of the third pereopods, al- 

 most directly opposite the female gonopores. 



The spermatophore of P. stylirostris differs 

 from all the others chiefly in the structure of the 

 sperm sac, which is largely formed by the dor- 

 somesial wall. This wall, after extending laterally, 

 is bent mesially in such a way as to reach, ven- 

 trally, the base of the mesial flap; as a result, part 

 of the ventral and lateral walls, apart from giving 

 support to the sac, serve as a protecting shield. The 

 spermatophore of P. stylirostris also possesses the 

 broadest wing to be found within the subgenus. 



484 



