PEREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



uropod situated distomesially according to her 

 figure 84. Antennae with alternating light and 

 dark red bands. In Formalin, body turns darker 

 red with ring around ocellus, garnet. Faxon (1893, 

 1895) noted that in specimens preserved in alcohol 

 there is a dark ring on the posterior part of the 

 branchial region and traces of color are present on 

 margins of rostrum, dorsal carinae, and append- 

 ages. In most specimens preserved in either 

 agent examined by me, the color pattern described 

 above is still distinguishable. 



Maximum size. — Males 17.5 mm cl, about 70 mm 

 tl; females 24 mm cl, 87.9 mm tl (Faxon 1893 and 

 Arana Espina and Mendez G. 1978; corroborated 

 by me). 



Geographic and bathymetric ranges. — Bahia 

 Magdalena (24°33'00"N, 112°00'30"W) to south- 

 ern tip of Baja California Sur, Mexico, throughout 

 the Gulf of California and southward to northeast 

 of Isla Maria Madre (22°00'N, 106°16'W), Nayarit, 

 Mexico; also from Champerico (13°55'36"N, 

 92°02'30"W), Guatemala, to Islas Lobos de Afuera 

 (06°45'S, 80°45'W), Peru (Fig. 52). It occurs at 

 depths between 16 and 400 m (shallowest cited by 

 Arana Espina and Mendez G. 1978), but most of 

 the recorded depths are <150 m. It occupies a large 

 variety of bottom types: sand, shell, sand and shell, 

 sand and mud, shell and mud, rock and mud, 

 green, grey and brown mud, broken gravel and 

 shells, and a mixture of mud, rocks, and coralline 

 detritus. 



Discussion. — Sicyonia picta is most similar to S. 

 disdorsalis; both are of moderate size and in addi- 

 tion bear a small epigastric tooth, a large posterior 

 tooth on the postrostral carina, and a strongly 

 developed one on the first abdominal somite. These 

 shrimps can be readily separated by their color 

 pattern and a number of morphological characters. 

 In S. disdorsalis an ocellus is lacking on the pos- 

 terior part of the branchiostegite, the rostrum is 

 slender throughout its entire length, and less ele- 

 vated than in S. picta, its inclination not exceed- 

 ing 20°; the epigastric and posterior teeth on the 

 postrostral carina are situated closer to the orbital 

 margin, between 0.06 and 0.12 (mean 0.10) cl and 

 0.55 and 0.65 (mean 0.60) cl, respectively; and the 

 posterior tooth rises from a uniformly low post- 

 rostral carina. 



The two species also differ in sculpture of the 

 abdomen. In S. disdorsalis the first abdominal 

 somite is traversed by a short anteromedian sul- 



cus which is not represented ventrally by a depres- 

 sion; the posterior tergal and posteromedian 

 pleural sulci of the second and third somites are 

 coalescent; the anteroventral extremities of the 

 second through fourth are unarmed or are pro- 

 duced in a small, ventrally projecting spine; and 

 the posteroventral extremities of first through 

 fourth somites are angular, that of the fourth bear- 

 ing a well-developed spine, and that of the fifth, 

 an extremely long one (instead of small as in S. 

 picta) in adults. 



In both species the petasma and the thelycum 

 also exhibit distinctive features. In S. disdorsalis 

 the distal projection of the distolateral lobule of 

 the petasma terminates in an acute tip rather 

 than being compressed laterally and produced in a 



• S. picta 



A S. disdorsalis 



* S. in gent is 



FIGURE 52.— Geographic distribution of Sicyonia picta, S. dis- 

 dorsalis, andS. ingentis. 



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