COPEPODA FROM IFALUK ATOLL 25 



Order Cyclopoida 



Suborder Gnathostoma 



Family Oithonidae Dana, 1853 



Genus Oithona Baird, 1843 

 Oithona {Dioithona) oculata Farran, 1913 



Oithona oculata Farran, 1913a, p. 188, pi. 30 (figs. 8, 9), pi. 31 (figs. 2-9). — 

 Rosendorn, 1917, p. 37, figs. 23a-g.— Kiefer, 1929, p. 10.— Dakin and Colefax, 

 1933, p. 208; 1940, p. 116, figs. 204a, b.— Sewell, 1947, p. 254.— Tanaka, 1960, 

 p. 60, pi. 26, figs. 5-10. 



Dioithona oculata. — Kiefer, 1935, p. 326. 



Material. — ^Loc. 194-E-5, a large number of adult females, some 

 males, and developmental stages: ad. 99, 0.53-0.60 mm.; ad. cf d^, 

 0.55-0.60 mm. 



Oithona minuta T. Scott, 1894, 0. rigida Giesbrecht, 1896, 0. oculata 

 Farran, 1913, and 0. alia (Kiefer, 1935) were united by Kiefer (.1935, 

 p. 322) in the genus Dioithona Kiefer, 1935, type species D. alia 

 Kiefer, 1935. The species of his new genus are characterized by the 

 presence of two setae on the (only) free segment of leg 5. One of 

 these setae is developed as in the genus Oithona (i.e., fine and long), 

 the second seta is short and spiniform; the development, moreover, 

 seems to differ in the 4 members of the new genus. Though recogniz- 

 ing the need for a further subdivision of the genus Oithona Bau'd, 1843, 

 sensu lato, I really must object to splitting off genera because of the 

 presence or absence of a very small seta, of very variable length too, 

 as long as this character is not coupled with such — and in my opinion 

 more important — characters as the development of the rostrum, 

 setation of the mandibular basipodite, and setation of the swimming 

 legs. I have, therefore, provisionally reduced the status of Kiefer's 

 genus to subgeneric level, awaiting a more thorough revision of the 

 Oithonidae. 



0. oculata Farran appears to be very closely allied to 0. alia (Kiefer, 

 1935) and only a very careful examination of the present specimens 

 has convinced me that they really belong to Farran's form, despite the 

 differences in length: Farran's female specimens are 0.90 mm., the 

 male 0.65 mm.; Kosendorn's female specimens are slightly shorter, 

 0.80 mm.; Tanaka's only female specimen measured 0.80 mm. 



Though smaller, the Ifaluk specimens are in complete conformity 

 with Farran's, Rosendorn's, and Tanaka's descriptions; they differ 

 from 0. alia in the following points: 



1. Bilobated gangliac mass in frontal part of head very prominent 

 feature in 0. oculata and fully absent in 0. alia. 



2. Endopodite of leg 4 comparatively long, reaching middle of 3rd 

 exopodal segment of that leg in 0. oculata. In 0. alia that endopodite 



