272 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 117 



the former the head is more rounded in dorsal view, the rostrum is 

 not so strongly curved, and the lateral marginal seta of the caudal 

 ramus is shorter than the ramus. Giesbrecht's descriptions of 0. 

 brevicornis are quite limited, and a detailed study of Hong Kong 

 specimens is badly needed. In addition to the difference in rostral 

 development, differences in the setae of B2 of the Md distinguish the 

 American 0. brevicornis from 0. hebes. In the former the marginal 

 setules are fewer and more widely spaced on the inner seta than on 

 the outer seta, whereas in 0. hebes the 2 setae are alike. In both 

 species, Hi bears 5 setae although Rosendorn (1917) shows only 4 

 setae in 0. brevicornis. 



Oithona hebes was very abundant in the Puerto Rican bays. It 

 was less numerous on the shelf but still ranked 4th among the copepods. 



Oithona nana Giesbrecht 



Figures 20c-g 



Oithona nana Giesbrecht, 1892, pp. 541-546, 549, pi. 4, fig. 8; pi. 34, figs. 10, 

 11, 20, 24, 26, 34, 35, 42; pi. 44, figs. 2, 6.— Williams, 1907, p. 72.— 

 Grandori, 1912, p. 14.— Gurney, 1927, pp. 159-160.— Carvalho, 1952, p. 

 167, pi. 2, figs. 95, 96.— Yamazi, 1956, p. 166, pi. 16, figs. 6A, B.— Grice, 

 1960a, p. 222; 1960b, pp. 487-488, figs. 7-11.— Tanaka, 1960, pp. 59-60, pi. 

 26, figs. 1-4.— Bjornberg, 1963, p. 75, fig. 39. 



Oithonina nana (Giesbrecht). — Sars, 1913, p. 5. — Wilson, 1932b, pp. 316-317, 

 figs. 190c-d.— Davis, 1950, p. 90.— Davis and Williams, 1950, pp. 523-525 

 (tables).— King, 1950, p. 130 (table) .—Woodmansee, 1958, pp. 254-255. 



Female. — Length 0.60-0.66 mm. Prosome:urosome = about 1.2. 

 Head truncate anteriorly. Rostrum absent. Anal segment shghtly 

 shorter than 2 preceding segments, about as long as caudal ramus. 

 Caudal ramus about 2.3 times as long as wide; lateral marginal seta 

 inserted shghtly proximal to middle of margin, about 0.8 as long as 

 ramus. Lateral apical seta short, about half as long as ramus. Al 

 reaches middle of pedigerous segment 3. B2 of Md with long terminal 

 seta armed on margins with strong setules and a much shorter slender 

 seta; Ri with 4 setae. Re of P1-P4 armed as follows: 

 Outer setae: 1-1-3, 1-1-3, 1-1-3, 1-1-2. 

 Inner setae: 1-1-4, 1-1-5, 1-1-5, 1-1-5. 



P5 with single terminal seta. 



Male. — Length 0.45-0.55 mm. Prosome:urosome = about 1.1. 

 Al typically folded as in 0. hebes. P5 and P6 with single terminal setae. 



Remarks. — 0. nana can be identified by the long urosome and Al 

 and the characteristic terminal seta on B2 of Md. The egg sacs are 

 characteristic, being oval, rather loose, and usually having more than 

 20 eggs in each. In the other bay species of Oithona, the sacs are 

 compact and have fewer eggs. 



