FISHERY BULLETIN: VOL. 75, NO. 2 



uropod armed with terminal, distolateral spine. 

 In males, petasma with ventral costa free from 

 distally flexible terminal part of ventrolateral 

 lobule; ventromedian lobule not expanded dis- 

 tally. Endopod of second pleopod bearing appen- 

 dices masculina and interna, and with basal 

 sclerite produced distally into elongate ventro- 

 lateral spur. Thelycum of open type, lacking 

 enclosed seminal receptacle. Pleurobranchia pres- 

 ent on somites IX to XIV; one or two rudimentary 

 arthrobranchiae on somite VII; and anterior and 

 posterior arthrobranchiae on somites VIII to XIII. 

 Podobranchia present on second maxilliped, and 

 epipod on second maxilliped (and on first if prox- 

 imal exite of coxa considered an epipod) through 

 fourth pereopod. 



List of species. -Western Atlantic: Pleoticus ro- 

 bustus (Smith 1885); Pleoticus muelleri (Bate 

 1888). Red Sea: Pleoticus steindachneri (Balss 

 1914). 



Affinities. -The members of Pleoticus resemble 

 those of Hymenopenaeus and Haliporoides in the 

 character of the rostrum and general form of the 

 carapace; however, in Pleoticus the epigastric 

 tooth is separated from the first rostral by an 

 interval which is equal to, or only slightly greater 

 than, that between the first and second rostral 

 teeth; an orbital spine is present as it only is in 

 the more distantly related Mesopenaeus; the 

 branchiocardiac carina is absent; and the branch- 

 iocardiac sulcus is usually absent. Furthermore, 

 the mandibular palp is two jointed unlike the 

 usually three jointed one of Haliporoides but like 

 that of Hymenopenaeus; however, in contrast to 

 the palp of the latter, that of Pleoticus is broad and 

 its distal article is as long as, or longer than, the 

 basal. Finally, in the petasma of Pleoticus the 

 distal extremity of the ventral costa is free from 

 the ventrolateral lobule instead of being fused 

 to it. 



Pleoticus agrees with Hadropenaeus in the 

 arrangement of the epigastric and rostral series 

 of teeth, the lack of branchiocardiac and post- 

 hepatic carinae, the absence of pterygostomian 

 spines, as well as in having the distal extremity 

 of the ventral costa of the petasma free from the 

 adjacent part of the ventrolateral lobule. The 

 considerably more elongate carapace, the low and 

 longer rostrum, and the presence of strong sub- 

 marginal carina, and orbital spine separate the 

 former from the latter. 



The similarities cited above indicate ihatPleoti- 

 cus occupies a position somewhat intermediate 

 between the more primitive Hymenopenaeus and 

 Haliporoides, on one hand, and Hadropenaeus on 

 the other. 



The genus Pleoticus is less homogeneous than 

 the other genera treated here. In P. robustus and 

 P. muelleri the branchiocardiac sulcus is abent or 

 indistinct whereas in P. steindachneri it is 

 distinctly marked; the branchiostegal spine, while 

 present in P. robustus and P. muelleri, is lacking 

 in P. steindachneri. Whereas in the petasma of 

 P. robustus and P. steindachneri the row of cincin- 

 nuli occupies almost the entire median line, and 

 the ventromedian lobule is distally membranous 

 and entire, in that of P. muelleri the row ofcincin- 

 nuli is limited to the proximal 0.4 of the median 

 line, and the ventromedian lobule is heavily scle- 

 rotized distally and bears strong projections. In 

 spite of these differences, it seems to me that the 

 many features shared by these species justify 

 their being grouped within a single genus. I have 

 not examined specimens of P. steindachneri, but 

 the descriptions and illustrations of Balss (1914, 

 1915) indicate that this shrimp is more closely 

 related to P. robustus and P. muelleri than to 

 members of other genera. 



Key to the Species of Pleoticus in 

 the western Atlantic 



1. Body entirely pubescent. Prosartema not 

 overreaching distal margin of first 

 antennular article. Branchiostegal 

 spine present. Females with paired, 

 triangular projections near anterior 

 margin of sternite XIV, and strong 

 median ridge on sternite XIII. Males 

 with petasma cincinnulate along en- 

 tire median line, its ventromedian 



lobule entire distally P. robustus 



Body almost entirely polished. Prosar- 

 tema considerably overreaching distal 

 margin of first antennular article. 

 Branchiostegal spine absent. Females 

 lacking triangular projections on ster- 

 nite XIV, bearing strong, median pro- 

 jection on sternite XIII. Males with 

 petasma cincinnulate along proximal 

 0.4 of median line, its ventromedian 

 lobule produced in two projections .... 

 P. muelleri 



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