COPEPODA FROM IFALUK ATOLL 155 



Adult female, total length 1.05 mm.; greatest diameter 0.26 mm.; 

 length of longest fm-cal seta 0.45 mm. The body of this specimen 

 was strongly cmi-ved and it could not be figured dorsally. 



Body strongly built, with robust cephalothorax, distinctly set off 

 from abdomen. Greatest diameter of cephalothorax in oral region, 

 rounded anteriorly and slightly narrowing posteriorly. Head and 1st 

 thoracic somite completely fused to form cephalic somite, which is 

 longer than combined lengths of thoracic somites 2 to 4. Line of back, 

 laterally, smoothly curving into well-developed rostrum, very prom- 

 inent structm-e of cephalic region (fig. 56a). Rostrum large, acutely 

 triangular with rounded apex, curved, pointing forward and slightly 

 downward, as long as fkst three antennular segments, separated from 

 cephalic somite by shallow groove. Lateral parts of cephalic somite, 

 specially in anterolateral parts, produced to cover basal parts of 

 oral appendages. Integument of back thickened in middorsal line 

 directly behind rostrum, forming internal trabecle opposite oral aper- 

 ture, apparently to provide ample surface for attachment of oral 

 muscles. Epimeral plates of thoracic somites 2 to 4 moderately 

 developed, cut off squarely. 



5th thoracic somite well developed, distinctly visible in lateral and 

 dorsal aspect. Length of abdomen equal to that of cephalothorax. 

 Genital somite (fig. 576) composed of fused abdominal somites 1 and 

 2, line of fusion very distinct dorsally and laterally, marked by row 

 of spinules. Abdominal somites 3 and 4 of equal length, anal (5th) 

 somite small, anal flap distinct, broadly rounded. 



All abdominal somites have spinules, distributed as follows : 



1st somite: row of spinules on each side, running obliquely upward 

 and forward; row along line of fusion, interrupted ventrally. 



2nd somite: 2 parallel, oblique rows of spinules on sides; closed 

 row of spinules along distal end. 



3rd somite: spinulation as 2nd. 



4th somite: oblique row of spinules on each side and closed row 

 along distal edge. 



5th (anal) somite : row along insertion of furcal rami. 



Furcal rami slightly shorter than diameter at base (proportion 

 13:17), slightly diverging. Internal margin nude, external margin 

 haired. 5 marginal setae and 1 appendicular seta on each ramus. 

 Setae 1, 5, and appendicular seta of moderate length, 1st with stiff 

 hairs along external margin. Seta 4 small, spiniform. Setae 2 and 3 

 greatly lengthened and thickened, especially 2nd, reaching half the 

 body length. Both 2nd and 3rd setae finely haired. 



Antennules (fig. 58a) short, half length of cephalothorax, 7-seg- 

 mented, 7th segment resulting from fusion of several small segments, 

 4th segment with weU-developed conical process obscuring 5th segment; 



