PfeREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



bands. Pereopods and pleopods pink. In addition, 

 spot — dark proximally, intense blue distally — 

 present on lateral ramus of uropods. Sosa Hernan- 

 dez et al. (1980) also presented color notes on 

 specimens from the Golfo de Tehuantepec: body 

 cream, suffused with reddish brown; carapace 

 bearing hook-shaped brown mark on each side; 

 lateral ramus of uropod with violet ventral spot; 

 antennae banded with violet with cream. In 

 Anonymous' (1980) work on the crustacean dec- 

 apods of the Gulf of California, the "9" is described 

 as purplish brown. 



Maximum size. — Male, 22.0 mm cl, 86.6 mm tl; 

 female, 28.5 mm cl, 100.7 mm tl (both recorded by 

 Arana Espina and Mendez G. 1978). Largest indi- 

 viduals examined by me: male, 21.4 mm cl, about 

 71 mm tl; female, 28 mm cl, about 89 mm tl. 



Geographic and bathymetric ranges. — Isla Santa 

 Margarita (24°20'00"N, 111°45'30"W - 24°20' 

 10"N, 111°46'40"W), Baja California Sur, Mexico, 

 to Cabo San Lucas, in the southern part of the Gulf 

 of California along both the east and west coasts, 

 and southward to Bahia Chamela (19°34'00"N, 

 105°07'24"W), Jalisco. Also from off Salina Cruz 

 (16°10'00"N, 95°00'00"W), Oaxaca, Mexico, to 

 Santa Maria (12°24'S), Peru, except off middle 

 Central America, Colombia, and most of Ecuador. 

 In the waters of Ecuador, it has been recorded from 

 the Golfo de Guayaquil and Islas Galapagos (Fig. 

 38). This species has been found at depths between 

 4-9 and 242 m, mostly at <85 m, on substrates of 

 sand and mud. 



The report of the occurrence of this shrimp in 

 Santa Maria, Peru, (Velez J., J. Zeballos, and M. 

 Mendez G., in press) is the first from waters south 

 of Bahia Sechura (5°43.1'S, 81°05.0'W), the 

 southernmost record cited by Arana Espina and 

 Mendez G. (1978). These specimens from Santa 

 Maria were collected at a depth of 10.5 m by A. 

 Robles on 28 June 1983. 



Discussion. — The closest relative of S. aliaffinis is 

 iS. affinis. The former, however, reaches a larger 

 size (about 29 mm cl) than S. affinis, the largest 

 known specimen of which has only a 17 mm 

 cl. Sicyonia aliaffinis also differs from S. affinis 

 in having a strongly buttressed antennal spine 

 and in the position of the first dorsal rostral tooth, 

 which is situated opposite or barely anterior to the 

 orbital margin instead of at about the anterior end 

 of the basal third of the rostrum. 



Differences in the abdominal characters are 

 even more striking. In S. aliaffinis the abdomen is 

 granulose, heavily so on the first three somites, 

 and the transverse sulci are deeply incised 

 whereas in S. affinis it is glabrous and bears weak 

 sulci, some of which are incomplete, adding to the 

 smooth appearance of the abdomen. In S. aliaffinis 

 the anteromedian sulcus of the first somite is long, 

 and although it becomes shallow ventral ly, it ex- 

 tends to near the ventral margin of the pleuron; in 

 S. affinis, in contrast, it is short, ending consider- 

 ably above the ventral margin of the pleuron. The 

 anteromedian sulci of the second and third somites 

 in iS. aliaffinis are long instead of short, recogniz- 

 able only on the ventral half of the somites; the 

 posteromedian sulci of these somites in S. 

 aliaffinis extend dorsally to a point at least at 0.25 

 of the height of the somite from the dorsal midline 

 and do not turn anteriorly, whereas in S. affinis 

 they extend only to about 0.35 from the dorsal 

 midline and turn anteriorly, delimiting ventrally a 

 weak longitudinal ridge which is absent in S. 

 aliaffinis. Also in iS. aliaffinis, the anterior tooth of 

 the first somite is acute but not curved at the tip as 

 it is in the other species, and the dorsal carina of 

 the fifth somite ends in a sharp angle or more often 

 in a tooth, whereas in S. affinis it slopes gradually 

 to the base of the caudal cleft. The anteroventral 

 extremities of the first through fourth pleura in S. 

 aliaffinis bear a small spine rather than being 

 unarmed. 



Features of the external genitalia also allow a 

 ready separation of these two species. In S. 

 aliaffinis, the distal projection of the ventrolateral 

 lobule of the petasma is bulbous dorsally; in con- 

 trast, that of S. affinis is comparatively thin. The 

 thelycal plate of sternite XIV is flat or very faintly 

 raised laterally in ill-defined elevations in S. 

 aliaffinis, whereas in S. affinis it bears a pair of 

 low but well-marked ovoid or subellipticai bulges. 



In addition to the morphological characters dis- 

 cussed above, S. aliaffinis exhibits a striking 

 9-shaped color pattern on the branchial region 

 which distinguishes it from all of its congeners 

 occurring in the American Pacific. 



Discussing the diagnostic characters of S. 

 aliaffinis, Burkenroad (1934a) stated that "The 

 carina of the second somite is, although not 

 notched above the juncture of the tergal sulci, 

 shallowly emarginate at this point." I have ob- 

 served that this carina may be entire or slightly 

 depressed either at the point where Burkenroad 

 noted it or more posteriorly; consequently, in this 

 shrimp the contour of the carina is insignificant. 



51 



