PEREZ FARFANTE: ROCK SHRIMP GENUS SICYONIA 



on second maxilliped. Epipod on first and second 

 maxillipeds and on first through third pereopods. 

 [Modified from Burkenroad (1934a, b) and Kubo 

 (1949).] 



The species of this genus (about 55), the only one 

 encompassed in the family Sicyoniidae, occur in 

 tropical, subtropical, and temperate waters. They 

 are marine, some invading brackish waters, and 

 abundant at shallow to moderate depths; a number 

 of them also range across the continental shelf 

 onto the upper slope, reaching depths of several 

 hundred meters. 



Members of Sicyonia exhibit a wide range of 

 intraspecific variation. The number and position of 

 the dorsal and apical rostral teeth and the ar- 

 rangement of teeth on the postrostral carina vary 

 as do the depth, extension, and form (continuous or 

 interrupted) of the abdominal sulci. Although the 

 number of the latter almost always provide a reli- 

 able diagnostic character for specific identifica- 

 tion, the posterior pleural sulcus may be present or 

 absent in some species. Furthermore, in females 

 the contour and sculpture of the thelycal plate of 

 sternite XIV and the shape of the posterior margin 

 of that of XIII also vary as pointed out in the 

 accounts for most of the species. In contrast, the 

 petasma of each of the members of the genus is 

 virtually invariable and thus useful for specific 

 recognition, and the appendix masculina is almost 

 constant in shape in all of the species. 



In the females, sternite XI is armed with a pair 

 of spines which vary considerably in length, rang- 

 ing from quite small, as in all members oi Sicyonia 

 occurring in the eastern Pacific, to extremely long, 

 as in the western Atlantic iS. olgae Perez Farfante 

 1980. The posterior thoracic ridge varies but 

 within a range that does not prevent its having at 

 least limited diagnostic value. 



Species of Sicyonia also exhibit various mor- 

 phological changes with increasing size. The 

 shape of the anteroventral margin of the pleuron 

 of the first abdominal somite may change gradu- 

 ally from straight in juveniles to pronouncedly 

 concave in adults, and the anteroventral ex- 

 tremities of the pleura of the first three or four 

 abdominal somites, from rounded to sharply 

 acute. The pleural armature, too, undergoes mod- 

 ifications with age; as Burkenroad (1934a) stated, 

 "A rounded angle usually precedes an unarmed 

 but acute angle, and this a veritable tooth, in the 

 course of individual development"; likewise, the 

 abdominal sculpture is altered, the sulci usually 

 becoming deeper as the animal grows. The forego- 

 ing statements indicate that abdominal features 



which are diagnostic for the identification of 

 adults have scant systematic usefulness in iden- 

 tify ing juveniles. 



Another characteristic of the genus is the wide 

 range in size among the species; whereas some are 

 small (the eastern Pacific S. disparri reaches a 

 maximum total length of about 44 mm), others are 

 quite large iS. ingentis and S. brevirostris attain a 

 total length of about 133 and 153 mm, respec- 

 tively). 



In the genus Sicyonia there are two series of 

 species the contrasting characters of which would 

 appear to justify their separation into two genera. 

 The members of one series (occurring on both sides 

 of the Atlantic, in the Mediterranean and Indo- 

 Pacific, and represented in the eastern Pacific by 

 S. disparri and S. laevigata) lack or occasionally 

 exhibit a very minute antennal spine, are armed 

 with basial and ischial spines on the first pair of 

 pereopods, bear an incision or a notch on the dor- 

 somedian carina of the second abdominal somite, 

 and usually display a conspicuous notch on the 

 lateral margin of the petasma. The members of the 

 other series (restricted to American waters) have a 

 well-developed, buttressed, antennal spine, lack 

 basial and ischial spines on the first pair of 

 pereopods, have no incision on the carina of the 

 second abdominal somite, and never bear a notch 

 on the lateral margin of the petasma. These two 

 series, representing extremes of the range of vari- 

 ation in members of the genus, were first recog- 

 nized by Burkenroad (1934a) as Division I and 

 Division II, respectively. Both in 1934a and 1945, 

 he stated that there are species or series of species 

 in which some of these characters are inter- 

 changed. Certain species (all from the Indo- 

 Pacific) that lack an antennal spine and in which 

 the first pair of pereopods are armed exhibit an 

 entire carina on the second abdominal somite (the 

 first two are characters of Division I, and the last of 

 Division II). At least one species (also occurring in 

 the Indo-Pacific) lacks an antennal spine and has 

 armed first pereopods (both characters of Division 

 I) but bears an unnotched carina (a feature of 

 Division II). Another species (the eastern Pacific 

 S. mixta) that possesses an antennal spine and has 

 armed first pereopods exhibits a clearly distinct 

 depression on the carina of the second abdominal 

 somite which seems to correspond to the notch 

 characteristic of Division I. 



Burkenroad (1934a) also divided his Division II 

 into species-groups, each named for one of the 

 species belonging to it. They were characterized by 

 the number, size, and position of the teeth on the 



