NO. 3583 COPEPODS — GRICE AND HULSEMAKN 11 



collected south of approximately 10°S, were probably obtained 

 from within the South Indian Deep water. The midwater trawl 

 (IK) also sampled this water during the greater part of each collection, 

 The North Indian Deep water, formed in the northern Arabian 

 Sea, is centered between 400 and 1500 m north of the Equator 

 and between 800 and 2000 m south of the Equator. Most of our 

 NV, Be, and IK samples collected north of about 10°S were probably 

 collected in this water mass. 



It thus appears from Ivanenkov and Gubin's (1960) work that no 

 sub-Antarctic water is present as such in the Arabian Sea. The con- 

 tinuity that apparently exists between the many species of copepods 

 in the western Indian Ocean and the North Atlantic is apparently due 

 to the transfer or movement of individuals from one water mass to 

 another. Obviously this must be an extremely slow process, but as 

 mentioned below, so might be the rate of speciation in these bathypela- 

 gic crustaceans. 



Since De Decker and Mombeck's comments relate mostly to the 

 occurrence of North Atlantic copepods (reported by Sewell, 1929, 1932, 

 from six midwater trawl samples) mainly in the eastern Indian Ocean, 

 where we have no samples, we are unable to compare their conclusions 

 with our data. It may, however, be premature to conclude as De 

 Decker and Mombeck did, that Atlantic Ocean copepods decrease in a 

 northerly and easterly direction in the Indian Ocean. The midwater 

 nets used by Sewell were made of "mosquito netting" and the number 

 of copepod species collected in the six hauls was quoted by De Decker 

 and Mombeck to be between only 1 and 54. 



Rather than emphasize the decrease of Atlantic Ocean copepods, 

 which our data fail to corroborate anyway, we wish to emphasize the 

 extremely widespread distribution of bathypelagic copepods. The 

 large number of our Indian Ocean species that are also common to the 

 Atlantic (241 in aU) is clear evidence for the effective dispersal of cope- 

 pods by deep currents, slow and sluggish as these may be. Ninety-two 

 percent of the deep-living species in the Arabian Sea, which is included 

 in the northernmost interval (p. 10), are also found in the North 

 Atlantic, some 8000 nautical miles distance. This high degree of simi- 

 larity in copepod species may indicate a slow rate of speciation in these 

 bathypelagic crustaceans, a suggestion that Day (1963) has already 

 made for planktonic organisms. 



Antarctic Species. — As indicated above, most of our collections 

 contained species that are widely distributed in the deep waters. 

 Certain of our collections obtained at the southern end of our samphng 

 area, however, contained species we did not find elsewhere. Although 

 few in number, these species have been included in a list of Antarctic 

 and sub-Antarctic copepod species compiled by Vervoort (1965). 



