CHAPTER VI 



Hydrachnellae Latreille, 1802 



(Hyclracarina) 



THE water mites form an ecological rather than a morphological 

 group. Some are swimming, while others are nonswimming. They 

 are inhabitants of fresh water except for the marine Pontarachnidae. 

 The marine Halacaridae, although closely allied to the Cunaxidae, are 

 also included here because of the habitat. The Hydrachnellae have 

 cuticular glands, stigmata and tracheae (with the exception of the 

 Pontarachnidae). Two pairs of eyes are present and may be either 

 separate or coalesced; an imperfectly developed median eye is also 

 pjresent at times. The tarsi usually possess two claws but are without 

 empodium or pretarsus. The palpi usually have five movable segments.. 

 The chelicerae have only the movable digit which is usually sickle- 

 shaped. The larvae, with the exception of Hydrovolziidae and Hal- 

 acaridae, are heteromorphous and have urstigma between coxae i 

 and II. 



The information on this group is taken from the works of Lundblad, 

 Viets, and Vitzthum. Although the European species are well known, 

 little has been done in this country except by Wolcott and later by 

 Marshall. However, neither of them has published comprehensive 

 works which will give the student an over-all grasp of the subject. 

 Little is known about the biology of 'the group as a whole, although 

 a few common species have been studied. Some work has been done 

 on the immature stages but here, as in many other groups, much rear- 

 ing work is needed. 



The brightly colored watermites are to be found in lakes or ponds, 

 along shores and in streams. A few are parasitic in the gills of fresh- 

 water mussels, and the larvae of other forms are parasitic on aquatic 

 insects much as chiggers are on vertebrates. Adult forms are preda- 



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