P6REZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



Figure 34. — Sicyonia penicillata, 9 23 mm cl, west of Punta 

 Tasca, Isla Santa Margarita, Baja California Sur, Mexico. 

 Thelycum. Scale = 1 mm. 



ington (1879) noted that "Color after two weeks 

 exposure to alcohol, bright red; with a dark red- 

 brown ocellated spot on each side of the carapace. 

 Antennae bluish." In many of the preserved speci- 

 mens that I have studied, the ocellus appears as a 

 dark circle. 



Maximum size. — Males 32 mm cl, about 103 mm 

 tl; females 35 mm cl, about 110 mm tl. 



Geographic and bathymetric ranges. — From 

 southwest of Punta Canoas (29°20'N, 115°02'W), 

 Baja California Norte, Mexico (Fig. 30), south- 

 ward to Bahia San Lucas, and in the Gulf of 

 California, from the northern end to Bahia Con- 

 cepcion on the west and northern Sinaloa on the 

 east; it seems to be absent from the southernmost 

 part of the Gulf. It has also been found off Pun- 

 tarenas (9'58'N, 84°50'W), Costa Rica (Boone 

 1930). This species occurs at depths between 0.60 

 and 180 m (latter by Boone 1930), mostly at 35-70 

 m. It has been recorded on sand (fine or coarse) and 



mud substrates that are sometimes densely cov- 

 ered with algae. 



Discussion. — The closest affinities of S. penicil- 

 lata seem to be with S. disedwardsi from which it 

 differs most conspicuously in features of the 

 petasma. The extremely long, slender, distal pro- 

 jections of both the dorsolateral (which bears a 

 lateral fiagellum) and ventrolateral lobules are far 

 different from the short, stout, and simple projec- 

 tions of the petasma of S. disedwardsi, as well as 

 from those of all other species of Sicyonia. These 

 two species also exhibit significant thelycal differ- 

 ences. In the thelycum of S. penicillata the lateral 

 bulges of the plate of sternite XIV are well defined; 

 the posteromedian emargination of the median 

 plate of sternite XIII is shallow (occasionally re- 

 placed by a longitudinal incision), often bears an 

 anterior notch, and is flanked by short posterolat- 

 eral processes marked basally by a conspicuous 

 transverse groove. In the thelycum of S. dised- 

 wardsi the bulges are low, often indistinct, the 

 posteromedian emargination of the median plate 

 of sternite XIII is broad and deep, lacks a notch, 

 and is flanked by relatively elongate posterolat- 

 eral processes which are delimited anteriorly by a 

 weak suture. 



The following characters are also helpful but 

 somewhat less reliable for distinguishing between 

 the two species. In S. penicillata the rostrum is 

 armed with only one tooth (rarely two) on the 

 dorsal margin, instead of two as in S. disedwardsi; 

 the stylocerite reaches the mesial base of the disto- 

 lateral spine of the first antennular article, 

 whereas in the latter species it often falls short of 

 the base; the dorsal extremity of the united pos- 

 terior tergal-posteromedian pleural sulci of the 

 first abdominal somite reaches the anterior mar- 

 gin of the somite, whereas in S. disedwardsi often 

 it does not; and the clearly defined although shal- 

 low posterior pleural sulci are usually present on 

 the first three abdominal somites of S. penicillata 

 but are quite weak or, more often, lacking on some 

 or all of the latter 



Fresh material of this shrimp may be identified 

 by a purplish brown spot on the branchiostegite, 

 sometimes bearing a yellow center with diffuse 

 border. 



Burkenroad (1934a) presented a detailed discus- 

 sion of the differences between S. penicillata and 

 the western Atlantic S. typica (as Sicyonia ed- 

 wardsii Miers, 1881). These species, which share 

 among other characters three teeth on the post- 

 rostral carina and usually one dorsal and two api- 



41 



