DECAPOD CRUSTACEANS OF THE WEST INDIES 27 



Brazil; furthermore, along the continental coasts of the Gulf and 

 Caribbean there is only one other member, S. reticulatum (Say), 

 ranging from Texas to Massachusetts. Inasmuch as several species 

 occiu" on the Pacific side of the Americas, a possible correlation might 

 exist between the relative paucity of Caribbean marine or quasi- 

 marine species of the subgenus and the depauperization of the Carib- 

 bean faunas following the elevation of the Panama Land Bridge in the 

 late Tertiary or early Pleistocene. 



Most of the Greater Antillean freshwater decapods apparently 

 have had their origins from stocks originating from the Central 

 American-Mexican region, and it is probable that the Jamaican 

 Sesarma did also. In light of the range of S. curacaoense, one might 

 suspect that a South American origin would seem more likely, but the 

 latter is so remotely related to the Jamaican species that it can hardly 

 be considered mth them. It is not inconceivable that two Central 

 American-Mexican stocks reached the Greater Antilles (both Cuba 

 and Jamaica) and that those reaching Cuba migrated eastward and 

 then southw^ard along the Lesser Antillean chain and subsequently 

 reached the South American continent. Obviously, however, too few 

 data are available to draw any definite conclusion. If, however, 

 S. curacaoense has had a South American origin, it would have had 

 an essentially unique history among the Greater Antillean decapods. 



HartnoU (1964) posed the question as to why "the grapsid crabs 

 evolved a population of species breeding in fresh water in Jamaica 

 but now^here else" and concluded that the absence of the Potamidae 

 [Pseudothelphusidae] is certainly a contributing factor. To what 

 extent the pseudothelphusids are actually in competition with Sesarma 

 elsewhere, however, remains to be demonstrated. His correlation, 

 nevertheless, is well taken. 



Unfortunately, the interrelationships of the members of the world- 

 wide genus Sesarma are poorly understood, and there are reasons for 

 questioning the validity of the subgeneric groupings as they are 

 presently recognized. Until a review of the entire genus has been 

 accomplished, little progress can be made toward an understanding of 

 the phylogeny of its members. 



As to the means utilized by the ancestral grapsids in reaching the 

 Antilles, since all of the ancestral forms probably had marine larvae, 

 a rafting hypothesis by no means seems essential, but in view of the 

 chance that the pseudothelphusid crabs and the crayfishes utUized 

 such in reaching the Antilles, some of the grapsids might also have 

 done so. The possibility that one or more stocks might have resorted 

 to rafting is supported by the observations of Marchand (1946) on 

 the accidental introduction of Platychirograpsus typicus Rathbun into 

 Florida. 



317-180—69 3 



