Savory - Arachnida 1977

186 Ill. PROLES ARACHNES
opisthosomatic somites, of which the last is incomplete, but in many
Palpatores the ninth and sometimes also the eighth somites are much
reduced or missing. In Laniatores there are generally nine sternites and
eight tergites with the operculum anale.
The general arrangement is that the first five tergites are fused together
into a single dorsal shield which is often also fused with the carapace.
The last three somites with the anal operculum are free and are usually
directed downward. The first sternite surrounds the genital orifice and
in general the second sternite is extended forward forming a long plate
which carries the genital orifice into a curious position not far behind
the mouth.
DISTRIBUTION
Although Opiliones are one of the orders whose distribution may be
summarized by the word ubiquitous, there are several features of
interest.
The Laniatores (Fig. 70) are the most highly specialized sub-order.
They number over 900 species and are the dominant group in southern
latitudes. Of the six families, Oncopodidae are a small group confined to
South-East Asia, while Cosmetidae and Gonyleptidae are found in
South and Central America and include almost a quarter of the suborder.
The Phalangodidae are widespread and are also the only
European family of the sub-order. Most of the species are small and
generally live in caves. The Triaenonychidae are found only in Australia
and Africa, where they are the dominant family in the southern African
fauna.
The Palpatores are only slightly less numerous than the Laniatores
and include all the familiar Opiliones of the north temperate regions.
They extend across the tropics, but are less numerous in hot countries
so that they are to this extent supplementary to the other sub-orders.
The Trogulidae are a family of slow-moving species, flattened in
form and generally found among moss or grass in damp situations. The
dorsal surface is covered with a long shield and the front edge of the
prosoma is prolonged into the spinous hood or camarostome characteristic
of the family. The Nemastomatidae have a moderately hard
epidermis and conspicuously long pedipalpi, usually without a claw.
The Ischyropsalidae are a small south European family, most generally
found in caves and in mountainous districts. Their peculiar feature is the
length of their chelicerae, which in some species are as long as the body.
The Acropsopilionidae contain one genus of one species from Chile,
and another also of one species from South Africa.
The Phalangiidae include all the commonest harvestmen of Europe
and North America, and are of very wide distribution.
24. THE ORDER OPILIONES 187
FrG. 70. Laniatores, dorsal aspect. After Berland. Species, Gonyleptes janthinus.
PALAEONTOLOGY
Fossil Opiliones are not unknown. From the Carboniferous comes the
genus Nemastomoides, with three species, N. elaveris, which has been
found both at Commenty in France and at Ellismuir in Scotland and
N. longipes and N. depressus, both from Illinois. The genus Dinopilio is
now placed among the spiders.
Seven genera of the family Phalangiidae are represented among the
ha:vestmen fou~d in Baltic amber, as well as two species from the
MI~cen~ of F~onssant. Among the most interesting is the species Caddo
dentz~alpzs. This genus is represented today by only two very rare species,
restncted to the eastern United States and Canada. It is characterized
by !arge ey:s on a low divided tubercle, and the fossil species is very
typical and IS closely allied to the living ones.
The su_b-order Laniatores has left us only one species, Gonyleptes
nemastomozdes, from Baltic amber.