PfeREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



on corals or other firm, rocky or shelly substrates, 

 but occasionally, as reported by Wass (1955), on 

 soft mud. 



On the basis of their samplings and the observa- 

 tions made by Lyons et al. (1971), Huff and Cobb 

 (1979) concluded that S. laevigata "shows some 

 preference for grass habitats in estuarine and 

 nearshore environments, associating with coarse 

 substrates further offshore where seagrasses are 

 absent." 



This species has been found at salinities be- 

 tween 22 and 37%o (Lyons et al. 1971 and Menzel 

 1956, respectively) and temperatures between 17° 

 and 32°C (Lyons et al. 1971 and Camp et al. 1977, 

 respectively). 



Discussion. — Sicyonia laevigata is most similar to 

 the Pacific S. disparri and the western Atlantic S. 

 parri, but it may be readily distinguished from 

 them by the following features. The epigastric 

 tooth in S. laevigata is smaller than, instead of 

 almost as large as, the other teeth on the postros- 

 tral carina. Also in S. laevigata this tooth is al- 

 ways situated anterior to the hepatic spine, be- 

 tween 0.06 and 0.16 (mean 0.12) cl from the orbital 

 margin, whereas in S. disparri it is often located 

 opposite or posterior to the hepatic spine but, if 



anterior, usually farther from the orbital margin, 

 between 0.12 and 0.25 (mean 0.17) cl. The an- 

 teromedian pleural sulcus of the first abdominal 

 somite in S. laevigata is short, commonly well 

 defined (sometimes obscure) dorsally, but obsolete, 

 cr represented by a shallow depression ventrally; 

 in contrast, in S. disparri and S. parri it is long, 

 extending to near the ventral margin of the 

 pleuron, although sometimes it is interrupted dor- 

 sal to midlength. In S. laevigata the posterior 

 pleural sulci are lacking, as they usually are in S. 

 disparri, whereas in S. parri they are present. 

 Furthermore, in the petasma of S. laevigata the 

 distal projection of the dorsolateral lobule is di- 

 rected distally, its tip curved dorsally, whereas in 

 S. disparri and S. parri it is strongly curved 

 mesially — but in the latter the tip is bent slightly 

 dorsally. It should be pointed out that S. parri , like 

 the other two species, lacks an antennal spine, 

 possesses a spine on the basis and ischium of the 

 first pereopod, and bears a dorsal incision on the 

 dorsomedian carina of the second abdominal so- 

 mite. 



Remarks. — In 1980, 1 stated that the dorsal mar- 

 gin of the rostrum of S. laevigata is armed with 

 three teeth, an opinion that was contrary to that of 



Figure 12. — CJeographic distribution of Sicyonia 

 laevigata, S. disparri, and S. mixta. 



15 



