Records of the Western Australian Museum 17: 455-460 (1996). 
Hesperopilio mainae, a new genus and species of harvestman from Western 
Australia (Opiliones: Caddidae: Acropsopilioninae) 
William A. Shear 
Department of Biology, Hampden-Sydney College, Hampden-Sydney, Virginia 23943, U.S.A. 
Abstract - Hesperopilio mainae, new genus and species, is described from 
Western Australia, based on specimens of both sexes. The new genus may be 
the most plesiomorphic of the subfamily. 
INTRODUCTION 
The opilionid genus Acropsopilio Silvestri (1904) 
was based on a Chilean species, A. chilensis 
Silvestri, and the genus was later used as a 
foundation for the family Acropsopilionidae by 
Roewer (1923). Soon, other acropsopilionine genera 
had been described: Caddella Hirst 1925, 
Oonopsopilio Lawrence 1931, Zeopsopilio Forster 
1948, Austropsopilio Forster 1955, and Tasmanopilio 
Hickman 1957. In my 1975 review of the group, I 
recognized the affinities of the acropsopilionids 
with the northern hemisphere caddids, and placed 
Acropsopilioninae as a subfamily of Caddidae 
Banks 1895. 1 proposed Oonopsopilio as a synonym 
of Caddella, Zeopsopilio of Acropsopilio, and 
Tasmanopilio of Austropsopilio (Shear 1975). This 
latter synonymy was not accepted by 
Cokendolpher and Maury (1990), who argued that 
the form of the eyemound differed. However, I 
maintain it because of the very strong resemblances 
of the palpi of the two "Tasmanopilio" species to 
those of other Austropsopilio. Since writing in 1975, 
I have seen specimens of Tasmanopilio fuscus 
Hickman, and am firm in upholding my earlier 
conclusions. The main point of difference regards 
the eyemound, which in mainland Australian and 
Chilean Austropsopilio bears eyes which are not 
much enlarged and which extends on a short stalk 
out over the chelicerae. In the Tasmanian species 
A. fuscus Hickman, the eyes are intermediate in size 
but the eyemound is extended forward, while in A. 
megalops Hickman, the eyemound is sessile and the 
eyes are almost proportionally as large as in 
Acropsopilio. 1 find this transformation series in the 
eyes and the close resemblance of the palpi 
convincing evidence for synomymy. 
The family Caddidae has one of the most 
interesting relictual distributions known. The 
subfamily Caddinae is known from eastern North 
America and Japan (Suzuki 1976); it consists of two 
living species, Caddo agilis Banks and C. pepperella 
Shear, and an Oligocene Baltic amber fossil, C. 
dentipalpis Koch and Berendt. I thought that the 
smaller species, C. pepperella, originated as a 
neotenic isolate of C. agilis as recently as 15,000 
years ago in adaptation to a shortened life cycle 
under periglacial conditions (Shear 1975). It so 
closely resembles juvenile C. agilis that even the 
type collection of the latter species was mixed. 
Suzuki (1976), in reporting both Caddo species from 
Japan, surmised that this could not be so, since 
there would be no way to account for the 
movement of C. pepperella from New England to 
Japan in so short a time. However, 1 think it 
entirely feasible that the Japanese populations are a 
second independent neotenic event, probably due 
to the same selection pressures. If this is true, 
although specimens from either population are 
indistinguishable in morphology, the Japanese 
isolate should have a new name. As an additional 
complication, both C. pepperella and C. agilis appear 
to be parthenogenic, with only three males of C. 
agilis ever reported among hundreds of specimens 
from many localities (Pennsylvania: Gruber 1974; 
Hokkaido: Suzuki and Tsurusaki 1983). However, 
given the Baltic Amber fossil C. dentipalpis, which 
seems nearly identical to living C. agilis, the 
Japanese and North American populations are 
probably relicts of a once much wider distribution 
for this species. 
Amongst the acropsopilionines, Caddella consists 
of four South African species and would appear to 
be the sister group of the other two genera, which 
are more closely related to each other. 
Austropsopilio contains six species described from 
Australia, and an indeterminate number of species 
from Chile (Cokendolpher and Maury 1990). 
Acropsopilio has six nominate species. Two occur in 
Chile, and specimens of the genus have also been 
collected in Argentina and Brazil (Cokendolpher 
and Maury 1990). The South American members of 
the genus need re-examination as there may be 
additional species. Single species of Acropsopilio 
occur in Mexico, northeastern North America, New 
Zealand, and Australia. 
With Acropsopilio and Austropsopilio already 
