Hydrachnellae 309 



Pionellinae Viets, 1937 



Genus: 



Pionella Viets, 1937 



Type. Pionella karamani Wiets, 1937 



Tiiihysinae Vitzthum, 1942 



Genera and subgenera: 



1. Tiphys Koch, 1836 



a. Tiphys s. str. (= Acercus Koch, 1842) 

 Type. Tiphys sagulatus Koch, 1837 



b. Acercopsis Viets, 1926 



Type. Acercus pistillifer Koenike, 1908 



c. Pionides Thor, 1901 



Type. Piona ensifera Koenike, 1895 



2. Hydrochoreutes Koch, IS31 

 Type. Spio ephippiata Koch, 1836 



3. Pionacercus V\eY?>\g, \^9A 



a. Pionacercus s. str. 



Type. Pionacercus leuckarti Piersig, 1894 



b. Pionacercopsis Viets, 1936 

 Type. Tiphys vatrax Koch, 1837 



4. Pionopsis Piersig, 1 894 



Type. Hydrachna lutescens Hermann, 1804 



5. Wettina Piersig, 1892 



Type. Tiphys podagricus Koch, 1837 (= Wettina macroplica Piersig, 

 1892) 



Astacocrotonidae Thor, 1927 



Figure 241 



Diagnosis: Astacocrotonids are parasitic in crab gills. Their skin is 

 weak and has no dorsal plates. In all probability there are no skin 

 pores, stigma, or trachea either. In the male eyes are present while 

 there are none in the mature female. The gnathosoma lies free between 

 the widely separated coxal plates i; all coxal plates are united on each 

 side and are contiguous. On each coxal plate iv a large gland appears 

 as shown in the figure. In the female the palpi are for grasping gill fila- 

 ments; the palpi are very short and thick — thicker than the legs. No 

 swimming hairs are on the legs and the tarsal claws are tridentated. 



