first postlarva, however, tlie supra-orbital spine 

 was almost always absent in P. d. duorarum, but 

 still present, although reduced, in P. setifenis. The 

 first \-entral teeth appeared when the number of 

 dorsal teeth had increased to 7, at about 10 to 11 

 mm. t.l. ; iwstlarvae with 8 to 10 dorsal and 2 ven- 

 tral teeth were 12.5 to 13.7 mm. lonsr. The variation 

 in length of the postlarvae within a single denti- 

 tion stage has been corroborated by Tabb, Dubrow, 

 and Jones ( 1962) in the population of Florida Bay. 

 Pink shrimp having six dorsal and no ventral 

 rostral teeth had a carapace from 1.7 to 2.3 mm. 

 long; the relation of length to dentition is most 

 variable in the seven-to-nine tooth stages when the 

 ventral teeth are being formed. 



Postlarvae of P. d. diwrarum under 12 mm. t.l. 

 were distinguished by Williams (1959) from those 

 of P. setifenis and P. a. aztecus (see under the lat- 

 ter subspecies). 



Juvenile P. d. duorarum, 18 mm. t.l. have shal- 

 low but distinctly long adrostral sulci and at 

 20 mm. t.l. the sulci are well developed. This char- 

 acter allows for a rapid separation of early juve- 

 niles of pink shrimp from those of the nongrooved 

 P. setifenis and P. schmltti. 



It is difficult to differentiate between the sexes in 

 .small specimens but, at a minimum of about 

 20 mm. t.l., males and females can be distinguished 

 by the shape and position of the endopods of the 

 first pair of pleopods. In the male the endopod is 

 located more proximally on the basis and is a little 

 longer than in the female. Small males can also 



be distinguished by the ridge on the midline of 

 sternite XIV (fig. 31a) ; in females sternite XIV 

 is drawn ventrally to a median point (fig. 31b). 

 Males 11 nun. c.l., 51 mm. t.l., with the petasmal 

 endopods still unjoined, usually have the ventral 

 costa with minute distomarginal spines and a few 

 teeth near the apex. (See also under Relation- 

 ships. ) 



GROWTH 



A number of studies on growth of P. d. duora- 

 ntm. at various phases of its life cycle have been 

 conducted. Among those concerned with larval 

 development, that of Ewald (1965b) is the most 

 complete. In the laboratory the larval phase was 

 comiDleted in 15 to 25 days, during which time the 

 animals grew from a first nauplius (about 0.4 mm. 

 t.l.) to a first postlarva (2.9 to 4.6 mm. t.l.). Ewald 

 also found in the laboratory that specimens from 

 6.9 to 9.4 mm. t.l. grew from 0.35 to 0.51 ram. t.l. 

 per day for 25 days. 



There are various estimates of growth rate in 

 juvenile and subadult pink shrimp. Tabb, Dubrow, 

 and Jones (1962), in length-frequency studies of 

 shrimp of northern Florida Bay, found that indi- 

 viduals of 6 mm. average c.l. increased at a 

 monthly rate of 2 mm. average c.l., and that the 

 rate increased to a maximum of 3 to 4 mm. monthly 

 until an average size of 20 mm. c.l. was reached. 

 Through mark-recapture studies, Costello and 

 Allen (1960) estimated that pink shrimp 16.7 mm. 

 mean c.l. in Florida Bay and adjacent waters grew 

 at a rate of 3.5 mm. mean c.l. per month. Kutkuhn 



1 mm. 



Figure Zl.—Penaeus (M.) duorarum duorarum Burkenroad. a. Sternites XIII and XIV, $ 5.5 mm. c.l., Tampa Bay, 



Fla. b. Sternites XIII and XIV, 2 5 mm. c.l., Tampa Bay, Fla. 



WESTERN ATLANTIC SHRIMPS OF GENUS PENAEVS 



515 



