241 



lost as it made their movement inside tlie salp difficult; this was com- 

 pensated by the development and ornamentation of receptor organs of 

 the basal segment of the flagellum, which apparently serves as an organ 

 of chemo- and rheotaxis while searching for salps in pelagic zones. 



All the species of Vibilia live in the surface layers of the water, most 

 of them distributed circumtropically, concentrating in places of mass 

 accumulation of the salps. Barnard (1930) had earlier predicted that with 

 the accumulation of new information, the number of species of Vibilia 

 might be reduced. In fact, the study of the collection, which provided 

 material for assessing individual, age, and geographic variability of some 

 species, as well as a review of the literature, convinced us that at present 

 15 species may be considered a reliable number. Two more species, viz., 

 V. bovallii Bonnier, 1896 and V. affinis Bate, 1862, have been included 

 in the key, although their validity is doubtful. V. peroni Milne-Edwards, 

 1830 and V. depilis Templeton, 1836 were described on the basis of 

 young specimens and so briefly that it is impossible to associate them 

 with any definite species. 



KEY TO SPECIES OF GENUS VIBILIA 



1 . Posterior lateral angles of last urosomite do not project backward . . 

 2. 



— Posterior lateral angles of last urosomite project backward along lat- 

 eral sides of telson 11. 



2. Process of 5th segment of pereopods II reaches end of 6th segment, 

 often extending beyond base of claw 3. 



— Process of 5th segment of pereopods II does not reach end of 6th 

 segment, extending only to 1/2-3/4 its length 5. 



3. Eyes absent. Antennae I very long, longer than head and first three 

 somites of pereon together 11. V. caeca Bui. 



— Eyes normally developed. Antennae I shorter than head and first three 

 somites of pereon 4. 



4. All pereopods thin and long; 4th segment not broadened; claws not 

 longer than 1/3 of preceding segment. Pereopods V-VI longer than 

 preceding pairs by 1/4 or more their length, mainly by virtue of 

 elongation of distal segments. Endopodite of uropods III in male 



broadened and considerably longer than exopodite 



4. V. antarctica Stebb. 



201 — Pereopods III-IV with strong broadened 4th segment, claw equal 

 in length to preceding segment or slightly shorter. Pereopods V-VI 

 longer than preceding pairs by 1/6-1/5 their length. Uropods III of 

 male and female with rami of equal length, endopodite not broad- 

 ened 2. V. viatrix Bov. 



5. Size of adults rarely exceeds 5 mm, on average 3-5 mm 6. 



