COPEPODA FROM IFALUK ATOLL 137 



Peltidium exiguum A. Scott, 1909 



Figures 46c,d, 49, 50 



Peltidium exiguum A. Scott, 1909, p. 204, pi. 65 (figs. 11-15).— Sewell, 1940, 

 pp. 143, 355, 363, 364.— NichoUs, 1941, p. 392.— Lang, 1948, p. 436, fig. 186 

 (no. 3). 



Material. — Loc. 588, 2 ad. 99, 1 ov., 0.65 and 0.66 mm.; 1 juv. 

 specimen, 0.48 mm. 



Description. — The following is based on the specimen (non- 

 ovigerous) of 0.66 mm. length, which also has been dissected and 

 mounted. 



Adult female, total length 0.66 mm.; greatest diameter 0.36 mm.; 

 length of longest f ureal seta 0.42 mm. 



Body strongly built, compressed dorsoventrally; in general outline 

 broadly ovate, very broadly rounded anteriorly (accentuated by 

 curious structure of rostrum), reaching greatest diameter at end of 

 cephalic somite and gradually tapering posteriorly (fig. 46c). Head 

 and 1st thoracic somite completely fused to form cephalic somite, 

 which is as long as combined length of thoracic somites 2 to 5. Epime- 

 ral plates of all thoracic somites (including 5th thoracic or 1st 

 abdominal portion and genital complex) with well-developed and 

 laterally produced epimeral plates. In lateral aspect, posterolateral 

 end of cephalic somite and epimeral plates of thoracic somites 2 to 5 

 and of genital complex are pointed (fig. 46f/); points directed caudally. 

 No trace of longitudinal median carina on cephalic somite, but carina 

 gradually develops on thoracic somites 3 to 5 and on genital complex 

 and distinctly noticeable in lateral aspect. On 3rd and 4th somites 

 carina preceded by small tubercle carrying hair. All somites and 

 genital complex with characteristic pattern of sclerotized ridges, 

 structure and position of which can best be seen in figure 46c. 



Genital complex, which as mentioned above has distinct epimeral 

 plates, apparently results from fusion of abdominal somites 1 to 3 ; it 

 is caudally produced in the middorsal line; produced part rounded 

 and covering part of 4th abdominal somite. Caudally produced 

 epimeral plates reach as far as middle of anal somite. Anal somite 

 about as long as preceding somite, anal flap invisible, caudally somite 

 is produced into knob in middorsal line, situated between rami of 

 furca (fig. 50a). 



Furcal rami parallel, each nearly twice as long as broad. Five 

 marginal setae and 1 appendicular seta. Seta 2 is lengthened and 

 thickened; it has a slightly swollen base. Remaining setae small; 5th 

 inserts halfway along external border. 



Rostrum broad, curved, platelike structure in front of cephalon. 

 Broad lateral sweeps of cephalic somite and dowaiward curve of 

 rostrum make it almost invisible from above, more so since rostral 



