Savory - Arachnida 1977

182 III. PROLES ARACHNES
are above the second coxae and are usually narrow oblique openings.
In Cyphophthalmi they are situated at the ends of small conical processes,
the coni foetidi, between the second and third pairs of coxae,
just behind the eyes. In the past the apertures of these glands have been
mistaken for spiracles and the glands themselves, which are often
visible through the carapace, for eyes. Hence Cyphophthalmi were
originally described as ha·ving stalked eyes. The glands secrete a fluid
when the animal is irritated. In many species the odour of the fluid is
not intense, and it has been variously described.
Simon (1879) wrote "chez les Phalangium opilio cette odeur rapelle
celle de brou de noix"; Rossler ( 1882) mentioned "an aromatic odour";
Bristowe said of Gonyleptidae that they produced a "strong rather sweet
smell"; and others have compared it to horseradish. Stipperger ( 1928)
described "an offensive odour, lasting for about two minutes", while
Blum and Edgar ( 1971) found that the secretion of two Leiobunum
species contained 4-methyl-3-heptanone.
The chelicerae are of the three segments, the first projecting forward
and the second downward at right angles to it. The second segment is
produced on its inner edge and the third is articulated outside this
process, forming a chela. These parts are pointed and finely toothed.
In Palpatores the chelicerae are not as a rule large, though they may be
somewhat elaborated in males (Fig. 65), but in many genera they are
conspicuously carried, stretched out in front and having sharp spines on
their inner surfaces.
The pedipalpi are of six segments (Fig. 66). The coxae bear gnathobases
which form part of the rather complex mouth: the other segments
FIG. 65. Phalangium, lateral aspect.
24. THE ORDER OPILIONES 183
Fw. 66. Pedipalp of Megabunus.
are different in the three sub-orders. In Palpatores the appendage is
relatively slender and almost always spineless. The tarsus usually carries
a claw, which when present is almost immovable and is quite short,
scarcely exceeding in length the width of the palp. The tarsus is longer
than the tibia when it bears a claw and shorter when it does not. In
Laniatores the pedipalpi are strong and armed with spines. The claws
are large and can be closed against the tarsus so that they act almost
like chelate organs.
The legs are of seven segments (Fig. 67). The first two pairs of coxae
generally carry gnathobases, but in some families these are borne by the
first pair only. The remaining segments are in some families no longer
than the legs of spiders, but in the majority they are characterized by
their extreme length, which indeed forms by far the most obvious feature
of most of the familiar Opiliones. In Laniatores and Palpatores the legs
of the first pair are the shortest, and the longest are the second pair in
Palpatores and the fourth in most Laniatores. In this sub-order these
posterior legs are often remarkably strong and stout with sharp spines
on the femora. The tarsal segments are many-jointed, the number ef
joints ranging from a few to a hundred or more. In the latter case the
tarsus becomes a delicate whip-like segment. In all Palpatores the tarsi
carry one claw; in Laniatores the two anterior pairs of legs, have also
one claw, while the two posterior pairs have two claws, sometimes pectinate.
As a rule the tarsal claws in this order are simple.
The mouth of Opiliones lies between an epistome above and a labium
below. The epistome projects from below the front edge of the carapace,
and sometimes, as in Nemastomatidae and others, is preceded by an
extra piece, the pre-epistome. The sides of the mouth are guarded by
the maxillary gnathobases of the pedipalpi and first legs, with the second
coxae sometimes as accessories behind them.