COPEPODA FROM IFALUK ATOLL 67 



Suborder Oligoarthra 

 Family Ectiiiosomidae G. O. Sars, 1903 



Geims Ectinosoma Boeck, 1865 

 Ectinosoma {Ectinosoma) dentatum Steuer, 1940 



Figures 19a,b, 20-22 



Ectinosoma dentatum Steuer, 1940, pp. 124, 128, 129, figs. 1-10.— Lang, 1948, 

 p. 205, fig. 114 (no. 4).— Bo^id, 1955, p. 4.— Noodt, 1955, p. 54.— Jakobiand 

 Nogueira, 1960, p. 4. 



Material. — Loc. 431, 1 ov. 9, 0.35 mm. Loc. 588, 1 ov. 9, 0.45 

 mm., 5 eggs; 1 ad. 9, 0.47 mm. Loc. 589, 1 ad. 9, 0.35 mm. (strongly 

 contracted); 1 ad. c^, 0.40 mm. (spermatophore visible in body). 

 Loc. 590, 5 ov. 99, 0.42-0.45 mm. (0.44), 3-6 eggs; 18 ad. 99, 0.41- 

 0.47 mm. (0.44); 3 ad. cTd", 0.32-0.38 mm. (0.36 mm). Loc. 591, 1 

 ad. 9, 0.45 mm. ; 2 ad. cT cf , 0.38 and 0.35 mm. Loc. 592, 1 ad. 9, 0.41 

 mm.; 2 ad. cT cf, 0.33 and 0.36 mm. 



Description. — 'The species unexpectedly proved to be fairly com- 

 mon in the Ifaluk collection. The following is based on a female and 

 a male from locality 592; both have been dissected and mounted. 



Adult female, total length 0.41 mm.; greatest diameter 0.09 mm.; 

 length of longest furcal seta 0.20 mm. 



General outhne of body in dorsal aspect spindle-shaped, greatest 

 diameter at end of cephalic somite; anterior part of body more or less 

 rounded, rostral base distinctly visible in front of head, posterior part 

 of body gradually tapering, without separation between cephalothorax 

 and abdomen (fig. 19g). Head and 1st thoracic somite completely 

 fused to form cephalic somite, which is slightly longer than combined 

 lengths of thoracic somites 2 to 4. Line of back, in lateral view, 

 smoothly curved into rostrum. Latter an elongated, triangular 

 plate; apex rounded, pointing downward and slightly forward. Row 

 of spines some distance from distal cephalic border, consisting of 

 8-10 threadhke spinules, sometimes very indistinctly visible and only 

 apparent after dissection. Sides of cephalic somite slightly produced 

 to cover basal parts of oral appendages. Thoracic somites 2 to 4 of 

 nearly equal length; in lateral view, with broadly rounded sides. No 

 spinules or hairs on thoracic somites. 



Genital somite (fig. I9b) composed of fused abdominal somites 1 

 and 2; line of fusion visible m dorsal and lateral aspect as chitinized 

 ridge, interrupted dorsally. Genital somite shorter than combined 

 lengths of abdominal somites 3 and 4, which have about same length. 

 No spinules of hairs on abdominal somites. 



Anal somite about half length of abdominal somite 4, deeply cleft; 

 anal flap broadly rounded, placed proximally. Furcal rami parallel, 

 about as long as wide. Each ramus carries 5 marginal setae and 1 



