258 PROCEEDINGS OF THE NATIONAL MUSEUM vor,. 117 



Acartia gracilis Herrick, 1887, p. 7. — Foster, 1904, pp. 75-76. 



Acartia giesbrechti Dahl, 1894, p. 13, figs. 15-18. — Bjornberg, 1963, p. 66. 



Acartia {Acanthacartia) giesbrechti Dahl. — Steuer, 1915, p. 396; 1923, p. 23, figs. 



102-105. 

 Acartia tonsa var. cryophylla Bjornberg, 1963, pp. 64-66, fig. 34. 



Female. — Length 0.87-0.97 mm. Rostral filaments present. Pro- 

 some :urosome = about 3.6. Posterior margins of PedSeg 5 smooth 

 or with dorsal series of minute spinules. Posterior margins of genital 

 and second urosome segments smooth or with a few dorsal spinules. 

 Caudal rami about 1.6 times as long as wide. Al reaching slightly 

 beyond posterior margin of genital segment, without hooks or spines. 

 Segment 2 of P5 with blunt process at anterior distal angle ; segment 

 3 about 1.5 times as long as segment 2 and subequal to seta on seg- 

 ment 2, with swollen base and conspicuous barbed section proximal to 

 slender tapered tip. 



Male. — Length 0.77-0.80 mm. LTrosome segments 1 and 5 with 

 lateral tufts of hair; dorsal posterior margins of segments 2-4 with 

 delicate spinules. Caudal rami about as long as wide. P5 as in 

 figure 11/. 



Distribution. — A. tonsa originally was described from Port Jack- 

 son, just north of Sydney, Australia. Since then it has been found 

 along both coasts of North and South America and, more recently, in 

 European waters, where it has been considered by some investigators 

 to be a recent immigrant. Its global distribution is summarized by 

 Remy (1927), who first discovered it in Europe. More recent reports 

 on its occurrence in Europe are summarized by Conover (1957) and 

 Schwarz (1960). Its distribution on the east coast of North America 

 north of Cape Hatteras is summarized by Bowman (1961), who over- 

 looked the 2 northernmost records, those of Steuer (1923) from the 

 Bay of Fundy, and of Bousfield (1955) from the Miramichi estuary, 

 New Brunswick. The most southern record in the western Atlantic 

 is that of T. Scott (1914) from the Falkland Islands. 



A. tonsa has been reported from 3 localities in the Indian Ocean: 

 Java Sea (Cleve, 1901), Maldives (Wolfenden, 1905), and just north 

 of the delta of the Indus River, 25° N., 67° E. (Cleve, 1904). These 

 records are unsupported by illustrations or discussion, and we con- 

 sider them highly questionable. In fact, there is some doubt in our 

 minds that the Acartia tonsa from Pacific South America described 

 by Giesbrecht is the one Dana described from Australia since Dana's 

 description was so lacking in detail and his species has not been found 

 for a second time along the Australian coast. 



In Bahia Fosforescente, A. tonsa was outnumbered only by Oithona 

 hebes. In the shelf area it was much less abundant and ranked 12th 

 among the copepods. 



