small that I consider each population to represent 

 a geographical subspecies ; thus, the name P. duo- 

 ranim dttorarum applies to the typical shrimp 

 (Perez Farfante, 1967). The two subspecies also 

 differ in the length of the third pereopod, which is 

 proportionately shorter in P. d. duorarum, than in 

 P. d. nofialis. 



Adult P. d. dtwrarum can be separated readily 

 from the closely related P. a. aztecus and P. brasi- 

 liensis. Females may be recognized by the undi- 

 vided median carina on the posterior process and 

 the slightly divergent anteromedian corners of the 

 lateral plates. Males may be distinguished by the 

 shape, the external spination, and tlie compact 

 group of very large, pointed teeth of the ventral 

 costa; the small, and either plain or sparsely 

 armed distal fold of the petasma, and also by the 

 appendix niasculina, which is stubby and broader 

 at the base than in P. a. aztecus and P. hi'asiliensis. 

 The shape of the ventral costa, which I recognized 

 as a diagnostic character for the first time, is a 

 striking feature by which the grooved species of 

 Penaeus from the western Atlantic and the Gulf 

 of Mexico may be distinguished. 



P. d. duaranim. also can be separated from P. a. 

 aztecus by its comparatively higher keel and nar- 

 rower dorsolateral sulcus; as stated above, the ra- 

 tio K/S in the former is usually over 3 (fig. 23) ; 

 in only about 5 percent of my sample was K/S 

 smaller. Pink shrimp also have a higher rostrum 

 which is usually straight rather than sinuous ; the 

 shape of the rostrum varies, however, and occa- 

 sionally specimens of P. d. duaranim have the tip 

 of the rostrum upturned (fig. 20b), and some P. a. 

 aztecus have a straight rostrum (fig. 39b). In ad- 

 dition, pink shrimp have a proportionately short- 



r.'l. 

 er rostrum than P. a. aztecus, the ratio — p vai-y- 



c.l. "^ 



ing from a maximum of 0.75 in the young to about 

 0.35 in individuals of 50 mm. c.l. ; the rostrum 

 reaching to the base of the thickened portion of 

 the lateral antennular flagellum in the young and 

 to the distal end of the first antennular segment in 

 specimens of 50 mm. c.l. The rostrum provides a 

 useful but not an entirely reliable character for 

 separating the two subspecies. 



The third pereopod is stouter and much shorter 

 in P. d. duorarum than in P. a. aztecus^ reaching 

 only to the distal end of the second and at most 

 exceeding the third antennular segment by the 

 entire dactyl. The merus and, particularly, the 

 carpus (fig. 29) are responsible for the shorter 

 length in P. d. duorarum, for the differences in the 

 lengths of the other podomeres of the third pei-eo- 

 pod are small (table 3). Tables 1 and 2 show the 

 lengths of the five distal podomeres ( dactyl to isch- 

 ium) of the third maxilliped and of the first pereo- 

 pod for three carapace-length intei-vals in P. a. 

 aztecus, P. d. duorarunn, and P. hrasiliensw ; no 

 significant differences in these characters are evi- 

 dent. Anothei- difference between the pink and 

 brown shrimps is the ratio Ijetween the lengths of 

 the carapace and abdomen, adult P. d. duorarum, 

 has a shorter abdomen. 



Tlie dark-colored spot on each side between the 

 third and fourth abdominal somites is generally 

 characteristic of P. d. duorarum; but many speci- 

 mens lack abdominal spots, and similar spots are 

 present not only in the otlier subspecies of P. 

 duorarum from the Antilles and Central and 

 South America, but also in P. hrasilieTisis and 

 occasionally in P. a. aztecus. Throughout much of 

 its range, P. d. duorarum lives in close proximity 

 with P. a. aztecus, and the presence of abdominal 

 spots cannot be used reliably to separate the two 



Table 1. — Ranges of lengths of distal five podomeres of third maxilliped in P. a. aztecus, P. d. duorarum, and P. brasiliensis 



of indicated intervals of carapace length 

 [Based upon a minimum of 30 specimensf or each subspecies and species] 



510 



U.S. FISH AND WILDLIFE SERVICE 



