A KEY TO THE AMERICAN PACIFIC SHRIMPS OF THE GENUS 



Trachypeiiaeus (DECAPODA, PENAEIDAE), 



WITH THE DESCRIPTION OF A NEW SPECIES 



Isabel Perez Farfante' 



ABSTRACT 



Study of American Pacific members of the genus Trachypertaetis reveals that variation in armature of 

 the telson includes not only movable spines, but also fixed spines and even no spines at all. It also con- 

 firms that the eighth somite bears two arthrobranchiae instead of one arthobranchia and one pleuro- 

 branchia. A new species, Trachypcnaeus fuscina, is described, the specific features of T. faoea Loesch 

 and Avila are presented, and a key to the five members of the genus occurring in the region, together 

 with their ranges, is included. 



Along the Pacific coast of Latin America species 

 of Penaeiis are the inainstay of the shrimp fish- 

 eries; however, members of various other genera 

 contribute to the catches in significant quantities. 

 Among the latter, three Trachypevaeus have 

 been previously recognized: T. byrdi Burken- 

 road, T. shnilis pacificus Burkenroad, and T. 

 faoea Loesch and Avila. A fourth, noncommer- 

 cial species, T. hrerisutume Burkenroad, is also 

 found in the region. Burkenroad ( 1934a, 1938) , 

 presented detailed descriptions of the taxa he 

 described, but the characters cited for T. faoea, 

 except color pattern, have not proven to be diag- 

 nostic. Since the commercial Trachypenaeus are 

 indiscriminately known by the common names 

 of "tigre" and "cebra," a definition of T. faoea 

 is needed. 



The study of collections of American Pacific 

 Trachypenaeus has shown that yet another com- 

 mercial species of this genus occurs in the area. 

 It also pointed out a previously undescribed var- 

 iation in the armature of the telson, and con- 

 firmed the identity of the gills on the eighth 

 somite. 



The measurement of total length is the linear 

 distance from tip of rostrum to posterior end of 

 telson, and that of carapace length is the distance 

 from orbital margin to midposterior margin of 



' National Marine Fisheries Service Systematics Lab- 

 oratory, U.S. National Museum, Washington, D.C. 20560. 



carapace. The ratio, length of posteriormost 

 pair of telsonic spines to width of terminal por- 

 tion of telson, is presented in the following man- 

 ner: length of spine/width of terminal portion 

 = average ratio {N, number of specimens: 

 range of variation). 



GENUS Trachypenaeus ALCOCK 



Trachypeneus Alcock, 1901: 15. — Burkenroad, 



1934a: 49.— Burkenroad, 1934b: 73, 94. 

 Trachypeiiaeus.— Kuho, 1949: 391.— Ball, 1957: 



202. 

 Type-species by original designation, Penaeiis 



anchoralis Bate, 1881. 



The telson of the genus Trachypenaeus was 

 described by Kubo (1949) as lacking fixed spines, 

 and by Ball (1957) as possessing several pairs 

 of lateral movable spines. Previously, Burken- 

 road (1934b) had proposed a grouping of the 

 genera of the subfamily Penaeinae in four series; 

 he defined the series Trachypenaeus as having 

 a variable number of mobile lateral spines on 

 the telson and characterized the series Parape- 

 naeus as possessing one to three pairs of movable 

 spines in addition to a fixed posterior pair, con- 

 sidering the presence of fixed spines on the telson 

 as a unique character for the latter series. 



In the species of Trachypenaeus described be- 

 low, however, the posteriormost of the four pairs 

 of spines on the telson is fixed, and in Trachy- 



Manuscrlpt accepted March 1971. 

 FISHERY BULLETIN: VOL. 69, NO. 3, 



685 



