FISHERY BULLETIN: VOL. 75, NO. 2 



FIGURE 61. — Mesopenaeus tropicalis, 9 25.5 mm cl, east of 

 Cayos de Albuquerque, western Caribbean. Thelycum, ventral 



abdomen with orange transverse rib at posterior 

 margin of sternites, interrupting overall trans- 

 lucent salmon. 



Although the color pattern described is altered 

 with the expansion and contraction of the chro- 

 matophores, this basic arrangement of colors was 

 usually recognizable in all specimens examined 

 by me. However, according to Iwai (1973), this 

 species exhibits an overall red in Brazilian waters. 



Maximum size.-Males: 20.5 mm cl; females: 

 28 mm cl. 



Geographic and bathymetric ranges-Northeast of 

 Cape Lookout, N.C. (34°43'N, 76°40'W), to the 

 Straits of Florida, and into the Gulf of Mexico to 

 Alabama. Also off the Bahamas, through the 

 Caribbean, and along the Atlantic coast of South 

 America as far as Rio Grande do Sul (Figure 34). 

 The record from Rio Grande do Sul (34°00'S) is 

 from Iwai (1973). This species occurs at depths 

 between 30 and 915 m (Figure 9), thus from rel- 



atively shallow waters (where it is infrequent) on 

 the continental shelf to the upper zone of the 

 continental slope. This bathymetric range is not 

 peculiar to M. tropicalis, but is also exhibited by 

 various other penaeoids. The single record of the 

 shrimp from northeast of Cape Catoche, and its 

 apparent absence in the Gulf of Mexico from Mis- 

 sissippi to northern Yucatan, suggest inadequate 

 sampling in the region. Its presence on the con- 

 tinental slope, even if only in the shallower zone, 

 where no barriers prevent its dispersion, also 

 favors this conclusion. 



According to the limited data at my disposal, in 

 the warm temperate waters of North America this 

 species tends to remain on the continental shelf, 

 where 85% of the samples examined by me were 

 caught; in contrast, off the Bahamas and to the 

 south, it seems to be more abundant off the shelf 

 edge, where 76% of the samples were taken. In 

 neither region do the animals appear to exhibit a 

 seasonal migration, moving from warmer waters 

 of the shelf to greater depth in late fall and 

 returning in the spring. 



Affinities .-Mesopenaeus tropicalis, ths sole mem- 

 ber of the genus, differs strikingly from the other 

 solenocerids occurring in the western Atlantic in 

 possessing antennular fiagella which are dis- 

 similar in shape, the dorsal one subcylindrical 

 and the ventral depressed. 



Variations in the relative length of the anten- 

 nular fiagella were pointed out by Lindner and 

 Anderson (1941). I have confirmed their observa- 

 tions and, in addition, have found that the range 

 of variations in North American populations is 

 different from that in populations occurring from 

 the Bahamas to Brazil, the former having longer 

 fiagella than the latter. Noteworthy is the paral- 

 lelism that exists in the relative length of the 

 antennular fiagella between Mesopenaeus tropi- 

 calis and two closely related allopatric species of 

 the genus Solenocera. Like the northern popula- 

 tion of M. tropicalis, S. vioscai, a North American 

 species, possesses longer fiagella than does S. 

 acuminata, which occurs from the Bahamas to 

 Brazil (Perez Farfante and Bullis 1973). A similar 

 tendency was observed by Perez Farfante and 

 Bullis in S. atlantidis, the northern populations 

 of which tend to have longer fiagella than do those 

 from the Bahamas southward. The thelycum of 

 M. tropicalis also exhibits considerable variation, 

 even within a single population, the shield of 

 sternite XIV varying from flat with the anterior 



338 



