543 



2nd, has barely bulged margins, the posterior one with sparse uniformly 

 distributed spinules; the 5th segment is shorter and narrower than the 

 preceding one; the 6th segment is longer than the 5th and approximately 

 438 equal to the 4th; the claw is barely curved and less than half the length of 

 the 6th segment. Pereopods IV are somewhat longer than pereopods III, 

 mainly because of the longer 2nd segment. Pereopods V are the longest; 

 the 2nd segment is straight and four-five times longer than wide; the 

 5th-6th segments are virgate, the 6th longer than the 5th but somewhat 

 shorter than the 4th and slightly curved; the claw is somewhat shorter 

 than half the length of the 6th segment. Pereopods VI are identical to 

 pereopods V but all the segments are somewhat shorter, especially the 

 4th-6th, and the 2nd is very slightly broader. The 2nd segment of pere- 

 opods VII is articulated with the inner side of the coxal plate and the 

 distal part of the pereopod does not protrude from under it; the apical 

 3rd segment is rudimentary; evidently as in other species of the genus, 

 the structure of pereopods VII may vary. 



The pleon is somewhat longer than the pereon. In epimeral plates I-II 

 the ventral and posterior margins diverge at an obtuse angle; the tip of 

 the posterior distal angle of epimeron III is strongly stretched backward. 



Urosomite I is more than half the length of urosomite II (geminate) 

 and often equal in length to the telson. The basipodite of uropods I 

 reaches the tip of the telson and is 2-2.5 times as long as the 

 exopodite; the endopodite is narrowly lanceolate and approximately half 

 the exopodite in length. Uropods II are narrower and shorter than other 

 pairs, reaching the tip of the telson; the exopodite resembles a small 

 spine. Uropods III are much longer than the telson; the endopodite is 

 not shorter than the telson; the exopodite resembles a spine. The telson 

 is not less than half the last urosomite in length, its tip rounded and with 

 fine denticles. 



Gills are present only on somites V-VI of the pereon. The oostegites, 

 as in R. brevicaudatum, are also poorly developed. 



Notes: Rhabdosoma minor and R. brevicaudatum are so close mor- 

 phologically and in some respects biologically (almost complete absence 

 of males in the population) that the separation of R. minor as an indepen- 

 dent species raises certain doubts. Knowing that the range of variation 

 in morphological characters (particularly the size proportions of various 

 structures) in the family Oxycephalidae is generally large, it is possi- 

 ble to visualise the described species as extreme forms of manifestation 

 of such variation at the borderline of subspecific differentiation. The 

 notable allopatric area of distribution of R. minor and R. brevicaudatum 

 also tends to confirm subspecific differentiation. The data presently avail- 

 able on the biology and distribution of these forms do not suffice for 

 resolution of this question. 



