New opilionid genus Hesperopilio 
457 
palpal setae are probably a basic character of 
opilionids, most acropsopilionines also have 
raptorial adaptations in the palpi. These seem 
minimized in H. mainae, while the glandular setae 
have become more important. 
The relationships of Hesperopilio are difficult to 
assess. Because the penis resembles that of 
caddines (the immediate outgroup) and some 
phalangiids (the next outgroup), it is possible that 
this genus is the most plesiomorphic of the 
subfamily. On the other hand, male genitalia have 
not been described for Acropsopilio. Some or all of 
the species of this genus may be parthenogenic, but 
only A. boopis of eastern North America has been 
collected in quantity without the discovery of 
males. Based on palpal and available penial 
characters, it would appear that a reasonable 
arrangement for the subfamily would be 
(((Hesperopilio ((Caddella ( Austropsopilio, 
Acropsopilio ))). 
Hesperopilio mainae sp. nov. 
Figures 1-9 
Material Examined 
Holotype 
8, Torbay Head (35°08'S, 117‘38'E), Lot 40 (refers 
to a block of land, not a group of specimens). 
Western Australia, Australia, 20 April-14 May 
1987, B. Y. Main (WAM 95/403). 
Paratypes 
Australia: Western Australia: 2 juveniles, same 
collection data as holotype, but 5 October-2 
November 1987 (WAM 95/404-5); 1 9, Stirling 
Range National Park, Bluff Knoll, 1070 m elevation 
(34 C 22'36.6''S, 118°15T0"E), 7 September 1995, S. 
Barrett (WAM 95/770); 1 8, same data as 
preceding 9 but 900 m elevation (34°20'56.1"S, 
118°14'54.7"E) (WAM 95/771); 1 8, Mt Lindsay, 
410 m, (34°50'30"S, 117°18 , 21"E), 31 August 1995, S. 
Barrett (WAM 95/768). 
Diagnosis 
See the generic diagnosis. 
Description 
Male 
1.25 mm long, 0.8 mm wide. Carapace about as 
broad as long, thoracic tergites not well marked, 
but with raised transverse ridge at posterior 
carapace margin; cuticle leathery, not heavily 
sclerotized. Eyemound nearly as wide as carapace 
(0.5 mm), strongly depressed between eyes, 
bearing series of five prominent tubercles over each 
eye. Eyemound not extending forward over 
chelicerae (Figures 1, 2). Ozopores not detected. 
Abdominal tergites not distinct, abdomen less 
voluminous than prosoma, soft. Abdominal 
sternites not distinct. Genital operculum (Figure 4) 
rounded, sparsely setose. Coxae and endites 
typical, similar to those of Acropsopilio species. 
Chelicera (Figure 5) stout, largely unarmed, basal 
article 0.17 mm wide, 0.36 mm long, distal article 
0.16 mm wide, 0.39 mm long. Fixed finger narrow, 
shorter than movable finger; movable finger 0.17 
Figures 3, 4 Hesperopilio mainae n. gen., n. sp., 8. 3, palpus, mesal view; 4, penis and genital operculum, ventral 
view. Scale line = 0.3 mm. 
