PEREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



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ances. Finally, the paired lateral bosses, repre- 

 senting the posterior component of the median 

 plate and each cut by a transverse suture, are 

 found only in S. ingentis. 



The "pencil of hairs" that Burkenroad (1938) 

 stated to be located on the dorsal surface of the 

 distal part of the ocular peduncle, near its disto- 

 lateral margin, actually is placed on the distome- 

 sial margin. He distinguished S. ingentis from S. 

 disdorsalis by, among other characters, the rela- 

 tive length of that tuft of setae, stating that in 

 large adults of the former species it overreaches 

 the eye whereas in S. disdorsalis it spans no more 

 than half the cornea. This character does not seem 

 to be a reliable one for, except in occasional speci- 

 mens of S. ingentis, in neither species does the tuft 

 surpass the eye. Burkenroad also considered the 

 disposition of the adrostral rib as a diagnostic fea- 

 ture that would serve to separate the two species. 

 Although in S. ingentis the rib lies parallel to the 

 ventral margin of the rostrum, in S. disdorsalis its 

 course varies: sometimes it is slightly arched near 

 the anterior end, as Burkenroad described it, but 

 often it is curved along the middle and occasion- 

 ally is slightly turned anterodorsally. The distance 

 of the rib from the ventral margin in the two 

 shrimps, however, exhibits a slight difference — in 

 S. ingentis it extends close to the margin whereas 

 in S. disdorsalis it lies more dorsally. 



The characters exhibited by S. ingentis, S. dis- 

 dorsalis, and S. picta suggest that they must have 

 diverged quite early from a common ancestor in 

 the group of species that share two teeth on the 

 postrostral carina. 



Notes on biology. — Herkelrath (1977) investigated 

 the temperature tolerance and age- growth and 

 length-weight relationships in this shrimp. He 

 found that within a salinity range of 33-35%o it 

 exhibits a wide range of tolerance to temperature 

 (4°-30°C). At a stressed salinity (261) this toler- 

 ance was considerably reduced (7°-25°), and mor- 

 tality increased proportionately with the duration 

 of exposure, regardless of temperature. His 

 studies indicated that shrimp with a total length 

 of 50-90 mm increased 10 mm per month and also 

 that there is no difference in length-weight ratio 

 between sexes. He also stated that among shrimp 

 "averaging 70 mm or greater in total length, the 

 average length of females was greater than that of 

 males." 



Anderson (1983) studied growth rates, molting, 

 and certain aspects of reproduction in a population 

 of S. ingentis occurring off Santa Barbara, CA. 



She found that spawning takes place far offshore 

 in deep water, about 145 m, and lasts from May 

 through October with the peak during the late 

 summer. She also observed that molt frequency is 

 highest in the winter and spring, that females do 

 not molt during the summer (the reproductive 

 period), and that males exhibit a similar pattern. 

 Size-frequency analyses based on monthly off- 

 shore and nearshore sampling indicated that ju- 

 veniles increased at a monthly rate of about 1-2 

 mo. 



Commercial importance. — There is a fishery for 

 this shrimp between Santa Barbara and Ventura, 

 Calif According to the California Department of 

 Fish and Game, landings in 1982 amounted to 

 127,000,956 lb with a value of $156,000,385. 

 Mathews (1981) stated that "Sicyonia ringens" is 

 occasionally fished in Magdalena Bay, which is 

 located on the ocean side of Baja California Sur. I 

 have little doubt that his remark applies to S. 

 ingentis and that "ringens" is an erroneous spell- 

 ing. Moreover, it seems to me almost certain that 

 the study of "Sicyonia sp." (distribution, abun- 

 dance, rate of growth, ratio total weight/total 

 length) in Magdalena Bay by Mathew and Gon- 

 zalez (1975), was based on a population of this 

 species, apparently the only abundant rock 

 shrimp in the area. However, because Magdalena 

 Bay is within the range of S. penicillata , another 

 species reaching sizes reported by the authors, it is 

 not possible to be certain of the identity of the 

 shrimp studied by them. It is indeed unfortunate 

 that the valuable information presented cannot be 

 definitely associated with a specific shrimp, par- 

 ticularly in view of the fact that so little is known 

 of the biology of any of the eastern Pacific rock 

 shrimps. Although S. ingentis is present in the 

 Gulf of California, it is not commercially exploited 

 there. 



Material. — 946 specimens from 52 lots. 



United States— California: 1?, CAS, 2 km W 

 of Moss Landing, Monterey Bay, 50 m, 23 Sep- 

 tember 1978, D. D. Chivers. IS 3$ , AHF, 5 km off 

 Point Mugu, 40-59 m, 25 April 1976, Velero IV stn 

 24833. Id , AHF, 8.4 km W of Venice, 70-73 m, 22 

 July 1958, J. L. Baxter. 1$, SIO, SW of Santa 

 Monica Bay, 22 March 1962, F H. Berry and H. C. 

 Perkins. 39 , SIO, San Pedro Bay 27 m, 20 March 

 1964, U.S. Fish and Wildlife Service staff. 16 46 , 

 SIO, N of Dana Point, 53-48 m, 29 March 1974, 

 Agassiz. 316 20V, JlO, off San Onofre, 54 m, 29 

 March 197 4, Agassiz. 26 29 , SIO, off San Onofre, 



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