Diagnostic Characters of Juveniles of the Shrimps 



Penaeus aztecus azfecus, P. duorarum duorarum, 



and P. brasiliensis 



(Crustacea, Decapoda, Penaeidaej 



By 



ISABEL PEREZ FARFANTE, Systematic Zoologist 



Bureau of Commercial Fisheries National Center for Systematics 

 U.S. National Museum 

 Washington, D.C. 20560 



ABSTRACT 



Illustrated tables are presented for the identification and sex determination of 

 juveniles (with carapace lengths of 8 mm. or more) of three grooved shrimps of 

 the genus Penaetis occurring in various areas along the North American Atlantic 

 coast, in the Gulf of Mexico, and in the Bermudas. Included is an account of the 

 development of the petasmata, thelyca, and appendices masculinae. 



INTRODUCTION 



Many investigations have been made of 

 juveniles of Pomeus that live in estuarine 

 waters along the Atlantic and Gulf coasts of 

 the United States. Particular attention has 

 been given to their movements, habits, growth 

 rates, and responses to fluctuations in temper- 

 ature and salinity. Such studies are continu- 

 ing in the United States and are now also 

 being made along the coasts of Mexico and 

 Central and South America; but despite the 

 attention that has been accorded these juveniles, 

 little progress has been made in ascertaining 

 characteristics that will permit their identi- 

 fication. 



Fortunately, the ranges of the two species 

 of nongrooved Penaetis, P. (Litopenaeus) seti- 

 fenis' and P. (Litopenaeus) schmitti, appar- 

 ently do not overlap, and therefore their identi- 



^ The species of Penaeus have been grouped by 

 Perez Farfante (1969) in four subgenera, two of 

 which are represented in American waters. The spe- 

 cies with short adrostral sulci and a thelycum of the 

 open type — in the western Atlantic P. setiferus and 



fication presents no problem; juveniles of these 

 species having a total length of 18 mm. or more 

 may be separated from the young grooved 

 shrimps by the short adrostal sulci. In con- 

 trast, the grooved Penaetis have overlapping 

 ranges, and the juveniles are superficially so 

 similar that identifying them has been almost 

 impossible heretofore. The purposes of this 

 investigation have been to study the develop- 

 ment of the juveniles of these grooved shrimps 

 and to discover characteristics that might al- 

 low their specific or subspecific determination. 

 The possibility of being able to recognize these 

 estuarine individuals permits more reliable 

 conclusions concerning the ecology and behav- 

 ior of the taxa represented, and aids in at- 

 tempts to predict the probable annual abund- 

 ance of each of them. 



P. schmitti — belong to the subgenus Litopenaeus, 

 and those species with long adrostral sulci, to Meli- 

 certus. The three taxa treated here belong to the 

 latter subgenus. 



