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BULUETIN 15 8, UNITED STATES NATIONAL MUSEUM 



and rarely in a combination of the two. On the ventral surface there 

 is also a large spot of coloring for each segment. In the first seg- 

 ment this lies along the median line and appears to be between 

 the bases of the mouth parts ; in the other segments it is very irregu- 

 larly arranged. The eye is deep red (Rathbun). 



Female. — Head separated from the first segment; fifth segment 

 with rounded posterior corners; first antennae reaching for about 

 three segments beyond the tips of the caudal rami ; distal margin of 

 the second segment of the basipod of the second, third, and fourth 

 legs armed with spines; inner margin of first basipod of fifth legs 

 concave and armed with small teeth. Total length, 2.75-6.5 mm. 



Male. — Considerably smaller than the female, the first antennae 

 straight and reaching 3 or 4 segments beyond the tips of the caudal 



rami. Fifth legs quite 

 asymmetrical, left basipod 

 and iDroximal segment of 

 the exopod elongated, the 

 distal exopod segment 

 shortened. No setae on 

 either exopod, but a fringe 

 of short hairs on the inner 

 margin of the left one, 

 which is considerably long- 

 er than the right. Total 

 length, 2.5-4 mm. 



Re-marks. — This is by far 

 the most abundant copepod 

 in the Woods Hole region, 

 and the one of greatest 

 economic importance. It is 

 much more a pelagic than a littoral species, but occurs abundantly 

 in Narragansett Bay, Buzzards Bay, Vineyard Sound, and even in 

 Woods Hole Harbor, particularly in winter and early in summer. 

 It has the habit of gathering in immense sw^arms or shoals, usually 

 offshore, so that its distribution is very irregular. For this reason it 

 is the only copepod of those here enumerated that is likely to consti- 

 tute an entire catch. Sars said that it sometimes occurs on the Nor- 

 wegian coast in such great numbers as to give the sea a reddish hue. 

 It is eagerly eaten by most food fishes during their development, and 

 by some, as the herring and mackerel, after they become adults. Its 

 large size combined with its great abundance makes it the most 

 important food of our plankton-feeding fishes. This copepod differs 

 from most calanids in that its eggs are deposited singly and float 

 about m the water until hatched. The eggs, the newly hatched 

 nauplii, and the various developmental stages are easily recognized 



Figure 10. — Calanus flnmarchicus: a. Female, dor- 

 sal ; 6, fifth legs. (From W. M. Wheeler) 



