69 



NOTES ON THE FREE-SWIMMING COPEPODS OF THE 



WATERS IN THE VICINITY OF THE GULF 



BIOLOGIC STATION, LOUISIANA. 



E. FOSTER. 



(Bead before the Louisiana aociety of Naturalists, December 12, 1903 ) 



The members of the order Copepoda form an important section 

 of that great class of animals known as the Crustacea ; important, 

 not only from the immensity of their number in individuals, but 

 as regards the variety of species represented. They are, for the 

 most part, very minute in size, and are free-swimming or parasitic 

 on fishes or other marine animals. With many of the parasitic 

 species, the nauplius or larval stage is free-swimming ; the species 

 becoming fixed to their respective hosts only during their later or 

 mature ^tate. Other forms may be termed semi-parasitic ; in other 

 words, in their mature state they may be able to swim from one 

 host to another, and thus, in some cases at least, may come under 

 the category of commensals rather than parasites. 



The order is not only found represented in the sea by an im- 

 mense number of individuals and a variety of species, but many 

 of its members have an exclusively fresh-water habitat, while 

 others, again, are to be found chiefly in the brackish-waters of the 

 marshes bordering on the sea, in the bays or in the estuaries of 

 tidal rivers. 



For the most part they are cosmopolitan as regards their geo- 

 graphical distribution, although it may be noted, that of at least 

 one fresh-water genus — Diaptomus — no species has, as yet, been 

 found common to the waters of this country and the Old World. 

 Wider investigations may prove, howvever, that even in the case 

 of this genus, members may be found which are cosmopolitan in 

 their range. 



Minute as these animals are in size, their immense numbers and 

 extraordinary fecundity mark them as perhaps the most important 

 of the whole of the Invertebrates from an economic point of view. 

 To the fish-culturist they are especially important, forming, as 

 they do, the primary food of the majority, if not of the whole 

 of our food-fishes ; and, if for no other reason than this, it is a 

 curious commentary on scientific research applied to practical ends 

 that so little has been done on the order by the zoologists of this 

 country. It is true that considerable systematic work has been 

 done as regards the fresh-water forms of the United States, espe- 



