COPEPODA FROM IFALUK ATOLL 273 



2nd segment of endopodite leg 2 with 2, 3rd segment of endopodite leg 4 

 with 3 appendages. Exopodite of leg 5 with 5 appendages. 



L. eulitoralis Noodt 



Leptomesochra pygmaea, new species 



Figures 110, HI 



Materlal. — Loc. 592, 1 ad. 9, 0.28 mm. 



Description. — The follomng is from the above-mentioned female 

 specimen (holotype), which has been dissected and mounted. 



Adult female, total length 0.28 mm.; greatest diameter 0.06 mm.; 

 length of longest furcal seta, 0.30 mm. 



General shape of body very slender, almost linear, especially in 

 dorsal aspect (fig. 110a). Division between cephalothorax and 

 abdomen very indistinct. Greatest diameter of body at end of 

 cephalic somite, almost imperceptibly narrowing posteriorly, anterior 

 part very slightly narrowing, rounded at antennular basis. Insertion 

 of antennules in rounded incision; between antennular bases very 

 small rostrum visible. Head and 1st thoracic somite completel}^ 

 fused, short, as long as combined lengths of thoracic somites 2 and 3; 

 back in lateral aspect very gently curved (fig. 1106). 



5th thoracic somite small, visible as narrow ring at anterior part of 

 abdomen, carrying very small 5th legs. 



Genital somite (fig. Ill/) composed of completely fused abdominal 

 somites 1 and 2; line of fusion visible at dorsolateral surface as 

 chitinized ridge. 3rd abdominal somite shorter than 4th. Some 

 spinules occur at distal part of ventral margins of genital and 3rd 

 abdommal somites. Anal somite shorter than 4th, deeply incised, 

 anal flap broadly rounded, in ver}^ proximal position. Furcal rami 

 as long as wide, completely nude. 5 marginal setae and 1 appendic- 

 ular seta on each ramus. Setae 1, 4, 5, and appendicular seta small 

 and fine, setae 2 and 3 thickened and lengthened, especially 2nd, 

 which surpasses total length of body. 



Antennules (fig. 111^) long and slender, reaching end of 2nd thoracic 

 somite, 8-segmented. Basal 4 segments are fairly long, distal 4 short; 

 segment 4 with small conical process, bearing aesthetasc and 2 setae. 



Antenna (fig. lllh) with basis and 1st eudopodal segment separate. 

 Exopodite styliform, 2-segmented, both segments with a seta. Endop- 

 odite with 5 setae and 2 spines. 



The dissection of the mouth parts in this small specimen proved to 

 be unsuccessful; the ventral aspect of the genital somite is represented 

 in figure 111/; there are two setae on the genital plates. 



Leg 1 (fig. Ilia) Avith 3-segmented exopodite and endopodite. 

 Basis small, with fine external seta and small internal spine. 1st 

 endopodal segment styliform, VA times as long as whole exopodite, 



