s 



260 Acarology 



ceous and feed on Crustacea, insect larvae, and other water animals 

 which are small enough to be captured. Some watermites are also para- 

 sitic in all stages in the gill chambers of crabs and are adapted for 

 grasping the gill filaments. They are to be found at all times of the 

 year but usually most of the species appear as adults in late summer 

 and fall. 



The Halacaridae, although closely related to the Cunaxidae, are 

 treated here with the true watermites because of the similarity of habi- 

 ^ tat and the relative ease of identifying them by their habits. 

 ^_ Keys (from Viets 1936) to the superfamilies and families are given. 

 Those who are interested in keys to the numerous subfamilies are re- 

 ferred to Viets. 



References: 



Only a few references are given. No attempt is made to make the list 

 comprehensive, since this is one of the most extensively worked groups and 

 a complete list is beyond the scope of this work. However, in the few 

 papers cited it is hoped that the reader can find the necessary leads to 

 understand the group better. 



Lundblad, O. 1927. Die Hydracarinen Schwedens. I. Zool. Bidr. Uppsala 



11:185-535. 

 . 1931. Sudamerikanische Hydracarinen. Zool. Bidr. Uppsala 13:1- 



86. 

 . 1941. Eine Ubersicht des Hydrachnellensystems und der bis jetzt 



bekannten Verbreitung der Gattungen dieser Gruppe. Zool. Bidr. 



Uppsala 20:359-379. 

 . 1941. Die Hydracarinenfauna SUdbrasiliens und Paraguays. Kungl. 



Svenska Vetenskapsakademiens Handlinger, Ser. 3, 19(7) : 1-183. 



. 1942. Ibid. 20(2):1-175; 20(8):1-171. 



Marshall, R. The complete works are needed for the study of the United 



States fauna; not comprehensive in nature. 

 Viets, K. 1936. Wassermilben oder Hydracarina (Hydrachnellae und Hal- 

 acaridae). Die Tierwelt Deutschlands 31:1-288; 32:289-574. 

 Wolcott, R. H. 1918. The Water Mites (Hydracarina). Chapter XXVI, 



pp. 851-875. In Ward and Whipple's Fresh Water Biology, John 



Wiley and Sons, Inc. 



Key to the Hydrachnellae Superfamilies ' 



1. Without genital suckers; red, nonswimming, living in the upper 

 courses of brooks Hydrovolziae 



With genital suckers (except marine forms) 2 



1 From Viets 1936. 



