FISHERY BULLETIN: VOL. 83, NO. 1 



Lucas (22°52'23"N, 109°53'23"W), Baja California 

 Sur (Fig. 12). This species occurs at depths between 

 0.2 and 82 m, mostly at <24 m, and on sandy 

 bottoms: sand, sand and shell, sand and gravel, 

 and a mixture of sand mud, and coral. Among the 

 eastern Pacific rock shrimps, S. disparri appears 

 to have one of the most restricted distributions, 

 being virtually confined to the Gulf of California 

 and waters off Nayarit. Its presence south of the 

 Gulf of California is reported here for the first 

 time. 



Discussion. — This shrimp is very similar to the 

 geminate western Atlantic S. parri both in mor- 

 phology and size. Burkenroad (1934a) first distin- 

 guished S. disparri by the absence of posterior 

 pleural sulci on the anterior two abdominal so- 

 mites and by the shorter, deeper, and more up- 

 turned rostrum. A few years later (1938), on the 

 basis of three additional specimens, he pointed out 

 other features in which S. disparri differed from 

 his two specimens of S. parri: the shape of the 

 posteroventral margin and extremity of the fourth 

 abdominal somite, the presence of one or two pairs 

 of movable spinules dorsal to the ventral margin of 

 the rostrum near its anterior end, and the presence 

 of four instead of three teeth on the dorsal margin 

 of the rostrum. He stated that these characters are 

 probably subject to variation and in so doing indi- 

 cated that they might not be diagnostic. He noted, 

 however, that the size and shape of the ocular 

 calathus and the size and disposition of the cornea 

 might prove to be diagnostic. 



My examination of a relatively large collection 

 of S. disparri has demonstrated that among the 

 various features that Burkenroad (1934a, 1938) 

 suggested to distinguish this species from S. parri , 

 three are diagnostic: 1) the disposition of the ros- 

 trum, which is upturned between 15° and 45° in 

 the former, is subhorizontal or inclined not more 

 than 13° in the latter; 2) the shape of the postero- 

 ventral extremity of the pleuron of the fourth ab- 

 dominal somite, which is angular in S. disparri 

 and rounded in S. parri; and 3) the shape of the 

 ocular calathus and the breath and disposition of 

 the cornea. In the Pacific shrimp the calathus is 

 broader than in the Atlantic species, the lateral 

 margin ranges from 0.50 to 0.60 (mean 0.54) its 

 width at the base of the cornea and the latter is 

 obliquely disposed. In S. parri the lateral margin 

 of the calathus (Fig. 15B) varies from 0.80 to 0.91 

 (mean 0.85) its width at the base of the cornea, and 

 the latter is almost horizontally disposed. I have 

 confirmed that the ratio of the lateral margin of 



the calathus to the length of the carapace is usu- 

 ally smaller in .S. disparri than in S. parri, rang- 

 ing from 0.08 to 0.13 (mean 0.11) in the former and 

 from 0.13 to 0.17 (mean 0.13) in the latter, but 

 sometimes overlapping. 



The absence of posterior pleural sulci is a 

 character that, although not infallible, serves al- 

 most always to separate S. disparri from S. parri, 

 lacking in all specimens of the former except in 

 two small individuals, in one of which traces of 

 them are present in the first three somites, and in 

 the other, in the second somite. In contrast, all 

 individuals of S. parri bear such sulci. As Burken- 

 road anticipated, the shape of the posteroventral 

 margin of the pleuron of the fourth somite, which 

 is usually concave in S. disparri and convex in S. 

 parri, is variable, sometimes straight in both 

 shrimps. 



The length of the rostrum is not a reliable diag- 

 nostic character, as previously suggested, only 

 tending to be slightly longer in S. disparri than in 

 S. parri — the ratio rl/cl ranges from 0.43 to 0.59 in 

 the former and 0.36 to 0.55 in the latter. It does 

 tend to be deeper, but not consistently, in the 

 Pacific than in the Atlantic species. 



Burkenroad (1938) also pointed out the presence 

 of a fourth tooth on the dorsal margin of the ros- 

 trum in four of his specimens of S. disparri, but he 

 considered this tooth to belong to the apical cluster 

 (as I have in the meristic data presented here) 

 when discussing differences in number of apical 

 teeth between his smaller male and the remaining 

 four shrimps. The number of apical teeth vary ii* 

 both species; however, more tend to be present in 

 S. disparri, 59% of the specimens possess more 

 than three teeth (57% four, 2% five), whereas in S. 

 parri 90% of them bear two or three (80% three, 

 10% two) and only 10% bear four teeth. In S. dis- 

 parri the rostrum seems always to be armed with 

 submarginal, movable spinules; their absence in a 

 few adults is probably due to loss by accident. But 

 among the specimens of S. parri I have examined, 

 only one from south of Joao Pessoa, Paraiba, 

 Brazil, bears a pair of such spinules. Another from 

 Varadero, Cuba, possesses a single, very minute 

 spinule located on the ventral margin of the ros- 

 trum, near the base of the ventralmost apical 

 tooth. 



The shape of the posteroventral margin of the 

 pleuron of the fourth abdominal somite is vari- 

 able, as Burkenroad predicted for S. disparri, 

 sometimes straight in both species, but, as stated 

 above, the posteroventral extremity is always an- 

 gular in S. disparri and rounded in S. parri. In the 



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