PEREZ FARFANTE: SPERMATOPHORES OF AMERICAN WHITE SHRIMPS 



laterally, whereas the other is spiniform-the tip 

 of the latter projection shows in Figure 5A at the 

 vertex of the emargination between anterior lobe 

 and the base of wing. 



The dorsal plate (Figure 6D) is almost as long as, 

 and lies against the dorsal surface of the blade; it 

 is produced in a central prominence that fits into 

 the concavity on the posterior extremity of the 

 anterior section of the blade. 



Thelycum (Figure 7) 



Sternite XIV is densely covered with setae ex- 

 cept over a pair of posterolateral crescentic eleva- 

 tions separated by a short, sharp posteromedian 

 ridge; this ridge is hidden in the adult by the 

 bulging surrounding area. The posterior portions 

 of the elevations are parallel to the thoracic ridge 

 which typically bears a pair of lateral prominences 

 provided with a brush of setae. Sternite XIII is 

 heavily sclerotized posteriorly forming a plate 

 with a broadly concave posteromedian margin not 

 overlapping sternite XIV, but with lateral 

 extremities produced into hornlike projections 

 freely overhanging sternite XIV. The central 

 region of the plate bears a strong rounded to sub- 

 conical knob and the posterior margin occasionally 

 is armed with a small median tooth. The anterior 

 part of sternite XIII is provided with a pair of 

 transverse folds, the mesial portions of which are 

 produced into sharply pointed conical projections 

 covered by minute setae. The strong posterior 

 ridge of sternite XII is divided by a median 

 depression, and its lateral extremities are 

 produced caudally in a pair of convexities hidden 

 by the scooplike coxal plates of the third 

 pereopods. These uniquely shaped coxal plates 

 support the sperm sacs anteriorly and seem to re- 

 tain, at least briefly, the sperm masses immedi- 

 ately after their release. It should be remembered 

 that the coxal plates are covered ventrally by the 

 bases of the anterior lobes of the spermatophores. 



Disposition of the Compound 

 Spermatophore on the Thelycum 



When the compound spermatophore is in posi- 

 tion on the female, the fanlike anterior lobes 

 become affixed to sternite XII with the lateral 

 portions lying beneath the coxae of the third 

 pereopods while their basal portions extend over 

 (ventrally) the coxal plates. The angular junctions 

 between the anterior lobes and the wings embrace 



Figure l.-Penaeus (Litopenaeus) occidentalis. Thelycum, $53.5 

 mm, cl, Golfo de Panama, Panama. 



the posterior extremity of the corresponding 

 female gonopore. The mesial borders of the 

 laminae, in turn, form supporting rims along the 

 lateral borders of the apertures of the respective 

 sperm sacs, and the flattened projections of the 

 laminae meet in the sagittal plane, while the 

 spiniform projections lie contiguous to the 

 posterior convexities of the anterior lobes (Figure 

 5C). The laminae extend laterally, adhering to the 

 posteroventral surface of the coxae of the third 

 pereopods, and the wings rest ventrally over and 

 against the laminae, both processes helping to 

 anchor the spermatophores to the thelycum. The 

 position assumed by the anterior part of the sper- 

 matophore on the female brings the apertures of 

 the sperm sacs to the coxal plates of the third 

 pereopods and thus close to the gqnopores; con- 

 sequently, it seems that the sperm might well ac- 

 cumulate on these spoonlike coxal plates. Whether 

 or not the opening of each sac is permanent, or 

 results from a rupture, has not been ascertained. 

 Posterior to the wings, the lateral blades press 



471 



