COPEPODA FROM IFALUK ATOLL 17 



Pseudocyclops pacificus, new species 



Figures 2-4 



Material. — Loc. 709, 1 ad. cf, 0.69 mm. 



Description. — The following is based on the specimen mentioned 

 above (holotype), which has been dissected and momited on slides. 



Adult male, total length 0.69 mm. Proportional length of cephalo- 

 thorax and abdomen 32 : 15. 



Small species with compactly built cephalothorax and compara- 

 tively long abdomen with long, strongly developed setae (figs. 2a, 6). 

 Head and 1st thoracic somite fused to form cephalic somite; no line 

 of fusion visible. Thoracic somites 4 and 5 separate. Cephalothorax 

 ovate m dorsal aspect. In lateral aspect cephalic somite anteriorly 

 broadly rounded, almost tumid, frontal part of head flat and running 

 into slender, one-pointed rostrum (fig. 2e). Line of back smoothly 

 curved. Distinctly pigmented spot between insertion of antennules 

 indicates well-developed eye, visible in preserved specimen in dorsal 

 and lateral aspects. 5th thoracic somite small, though better developed 

 than in P. obtusatus, well separated from 4th, visible as a narrow 

 band in dorsal view; lateral margins of 5th somite rounded, covering 

 about half the genital somite. 



Abdomen 5-segmented; 1st (genital) somite nearly symmetrical, 

 genital aperture on left side. 1st to 4th abdominal somites of nearly 

 equal length, slightly telescoped in present specimen (figs. 2c,d). The 

 various somites and the fm*ca have the following proportional lengths: 



somite 12 3 4 5 furca 



15 24 24 19 7 11 =100. 



Anal somite small, anal operculum armed with 4 spines, visible in 

 lateral and dorsal aspect. In lateral aspect largest spines reach be- 

 yond middle of furca. In dorsal aspect structure of spines can best 

 be observed; 2 small median spines flanked by much larger spine on 

 left and right sides (figs. 2c, d). 



Furcal rami about as long as broad. Four spiniform setae on each 

 ramus and small, external, setiform spine. Seta 1 slender, about as 

 long as abdomen, haired. Seta 2 long and strong, about twice as 

 long as abdomen, haired, basal part nude, armed with 3 strong spines 

 on external and 2 strong spinules on internal margin. Seta 3 slightly 

 shorter than 2nd seta, at base of external border, with strong tooth; 

 basal part of internal margin set with spiniform hairs gradually in- 

 creasing in size distally. Kemainder of seta haired. Seta 4 almost 

 as 1st, shorter, also haired. External setiform spine nude (figs. 2c,d). 



Antennules short, not quite reaching end of cephalic somite. They 

 are 18-segmented; antennule on left side normally developed, on right 



