Australian Arrenurus 
257 
conical hump. D1 on a hump, D2 lateral of this 
hump on posterior dorsal body part. Medial 
margin of CX3 longer than medial margin of CX4; 
CX4 without posteromedial comer. Gonopore 58 
long. Genital plates long and bowed, extending 
onto lateral sides of body (Figure 70). Petiole a 
protrusible hyaline, tube-like structure, open 
posteriorly, at basis with a scissor-like 
sclerotization (Figure 71). Lengths of PI-PV: 36, 98, 
72, 110, 53. PII with 4 setae on medial side; PIV 
with a rounded anteroventral comer (Figure 73). 
Lengths of I-leg-4-6: 165, 150, 136. Lengths of IV- 
leg-4-6: 281, 170, 184; IV-leg-4 without a spur; 
second, third and fourth legs with numerous 
swimming setae. 
Female 
Unknown. 
Remarks 
A. gereckei can be separated from the A. tripartitus 
by its body colour, the large, conical hump on the 
posterior dorsal body part and the shape of the 
body (ventral posterior body part less extending 
beyond dorsal posterior body part). 
Etymology 
The species is named after Dr R. Gerecke. 
ACKNOWLEDGEMENTS 
I am indebted to Dr M.S. Harvey for his help 
with the preparations for this trip and for his 
comments on the manuscript, to the Department of 
Conservation and Land Management (Perth), the 
Australian National Parks and Wildlife Service 
(Darwin) and the Conservation Commission of the 
Northern Territory (Palmerston) for their 
permission to collect water mites in the national 
parks of Western Australia and Northern Territory, 
to G.M. van der Pal for her assistance with the 
fieldwork and to Dr M. Grasshoff (SMF) for the 
loan of type material of A. thienemanni. 
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