DISCUSSION OF SPECIES 

 (Alphabttic.illy Arranged) 



Since this paper deals chiefly with the geographical and 

 vertical distribution of the copepod species, they are here 

 arranged for convenient reference in alphabetical order 

 without reference to their systematic relationships. The 

 number of new species is small considering the thousands 

 of specimens examined, but is all that could be expected 

 in tows made so near the surface of the ocean. 



Attention has been concentrated particularly on dis- 

 covering the reactions of a long list of known species of 

 copepods to temperature, salinity, hydrogen-ion concen- 

 tration, and light in their native habitat. A surprising 

 amount of information along these lines may be extracted 

 from the station records above, and this has been pre- 

 sented according to species in the discussion that follows. 



[The bibliographic references to the original publica- 

 tion of each species given in this paper did not appear in 

 the original manuscript submitted to the Institution. They 

 have been assembled and verified by Miss Lucile McCain, 

 of the Division of Marine Invertebrates, U. S. National 

 Museum. In the case of species amplified by Dana and 

 Giesbrecht in their larger monographs (in ii'^53-iS55 and 

 1892 respectively), reference to these particular works is 

 also' made, as well as to the very brief original descrip- 

 tions. — Ed.] 



Genus ACARTIA Dana, 1846 



Acartia claiisii Giesbrecht 



[Acarlia claiisii Giesbrecht, Atti R. Accad. Lincei, Rome, ser. 4, 

 vol. 5, sem. 2, p. 25, 1S89: Fauna unci Flora des Golfes von 

 Neapel, vol. 19, pp. 508, 522, pi. 30, figs. 2, 6, 9, 13-15, 17, 

 28, 36, 37; pi. 31, figs. 36, 37; pi. 42, fig. 32; pi. 43, figs. 3, 5, 

 14, 1892.] 



Found at only four scattered stations in the central and 

 northern Pacific, but more common in the northern Atlantic. 

 It was taken in 7 nocturnal and 7 diurnal surface tows, 4 

 50-meter tows, and 5 loo-mcter tows. All the Carnegie speci- 

 mens taken in northern latitudes were at the surface or in 

 the 50-meter tows; those found in the tropics were in the 

 two deeper tows. It is worthy of note that this species was not 

 recorded in the Challenger or the Siboga expedition, nor 

 from any Pacific station in Sars' (1925) "Bathypelagic cope- 

 pods."' It would seem, therefore, to be more or less indifferent 

 or possibly somewhat positive to the weaker light of northern 

 regions, but becomes negative to the strong light of the 

 tropics. 



Acartia danae Giesbrecht 



\Acartia danae Giesbrecht, Atti R. Accad. Lincei, Rome, ser. 4, 

 vol. 5, sem. 2, p. 2fi, 1889; Fauna und Flora des Golfes von 

 Neapel, vol. 19, pp. 508, 522, pi. 30, figs, i, 23; pi. 43, fig. 8, 

 1892.] 



Not obtained at any of the .Atlantic localities, but widely 

 distributed and often very abundant in the Pacific. With 

 minor exceptions there are two notable gaps in its dispersion 

 in the latter ocean, one from station 48 to 61 in the south- 

 eastern region and the other from station 116 to 131 in the 

 region north of 40° parallel of latitude. It was present in 19 

 nocturnal and 46 diurnal surface tows, 77 50-meter tows, and 

 60 loo-meter tows, and in the vertical tow from 1000 meters 

 at station 64. This would indicate, as in the previous species, 

 more or less indifference to ordinary light with a definite 

 downward movement when the light becomes stronger. The 

 species is readily recognized by the strong spines at the 

 posterior corners of the fifth thoracic segment. 



Acartia longiremis (Lill)eborg) 



[Dias longiremis Lilljeborg, De crustaceis ex ordinibus tribus: 

 Cladocera, Ostracoda et Copepoda, in Scania occurrenfibus, 

 p. 181, pi. 24, 1853.] 



Present at nearly every locality in the Sargasso and Carib- 

 bean regions, but confined to a few stations in the Pacific, 

 north of the Samoan Islands. It was found in i nocturnal and 

 10 diurnal surface tows, 11 50-meter tows, and 14 loo-meter 

 tows. So far as the present vertical distribution indicates, it 

 is practically indifferent to light. Sars (1903, p. 149) stated 

 that this species sometimes occurs in great numbers along the 

 Norwegian coast, but no trace of such gregarious com- 

 munities was found in the present plankton. 



Acartia negligens Dana 



[Acartia negligens Dana, Proc. Amer. Acad. Arts and Sci., vol. 

 2, p. 26, 1849; U. S. Exploring Exped., 1S38-1842 (Wilkes), 

 vol. 14, pt. 2, Crustacea, p. 1121, 1853; pi. 79, fig. ■^a-c, 1855.] 



Not present in the Atlantic plankton; in the Pacific it was 

 well distributed in the eastern and southeastern parts but 

 everywhere else extremely straggling, with an appearance at 

 one or two consecutive localities and long intermediate 

 stretches of total absence from the plankton. It was taken in 

 16 nocturnal and 25 diurnal surface tows, 27 50-meter tows, 

 and 27 100-meter tows; also in the vertical tow from 1000 

 meters, station 64. Such a vertical distribution indicates even 

 more indifference to light than in any of the preceding 

 species, and this conclusion is strengthened by the fact that 

 the species was often found equally distributed in all three 

 tows at the same time. 



Genus ACROCALANUS Giesbrecht, 1888 



This genus was not found in the Atlantic plankton ob- 

 tained by the Carnegie, but the species longicornis has been 

 reported from the North Atlantic. Four species of the genus 

 were found quite abundantly in the Pacific, one or more 

 occurring in every region, so that the genus cannot be desig- 



169 



