CHAPTER X 



CLASS CRUSTACEA: SUBCLASS COPEPODA : ORDER 

 EUCOPEPODA: GENUS CYCLOPS: WATER FLEAS 



THE class Crustacea, which includes such familiar animals as the crabs, 

 lobsters, shrimps and wood-lice, contains also a host of small aquatic 

 arthropods, among which are the water fleas (Cyclops), so named on 

 account of their short, jerky movements when swimming. The subclass 

 Copepoda in which the genus Cyclops is placed contains a great variety 

 of crustaceans with very diverse life histories ; some are ectoparasites 

 of marine animals, as for instance the common Argulus, or Carp louse, 

 a flat, leaf-shaped form provided with suckers by which it fixes itself 

 to fish ; others are endoparasites and live in such situations as the 

 mouth and under the skin of fish. Many of these parasitic forms 

 illustrate the degeneration of structure which so often accompanies the 

 assumption of the parasitic habit. 



The great majority of copepods are free-living and are for the most 

 part of small size ; they are abundant in both fresh and salt water in all 

 parts of the globe ; the species belonging to the genus Cyclops are the 

 only copepods which are of known importance. For a general account 

 of the class the reader is referred to the article in Lankester's Treatise 

 on Zoology, Part 7, fasc. III. 



GENUS CYCLOPS 



Minute Eucopepoda in which the first thoracic segment is united to the 

 six head segments to form a cephalothorax, which is covered by a carapace 

 produced into a rostrum in front, and which bears on its dorsal surface 

 a median eye; tlie cephalothorax is armed with diverse appendages. 

 There are in addition five free segments, each provided with a biramose 

 swimming leg ; the sixth thoracic segment bears the sexual opening and in 

 the female is united with the first abdominal segment. There are four 

 abdominal segments, the fourth of which has on its dorsal surface the 

 anus, and at its termination a pair of stylets, the caudal fork, produced 

 into feathery plumes. 

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