Savory - Arachnida 1977

134 Ill. PROLES ARACHNES
to be seen below. The sternum is in three pieces; there is no labium, and
the first visible sternite is a triangular piece lying between the first
coxae and representing stcrnites 3 and 4. Behind it arc two much smaller
pieces, reduced in size by the approach of the coxae to the middle line.
On the lower side of the opisthosoma, the stcrnite of the second somite
is very large. It carries the openings of the first pair of book-lungs, and
the genital orifice is on its posterior margin. The second pair of booklungs
open on the third stcrnitc; both this and the fourth are much
narrower than the six which follow, and of which the first four are
marked by muscular indentations.
The chclicnae are of two segments and are not chelate (Fig. 39).
The proximal segments lie parallel to one another and have a certain
15. THE ORDER UROPYGI 135
FrG. 39. Chelicera of Thelyphonus. After Kaestncr.
degree of longitudinal freedom, as well as the ordinary ability to mcve
sideways. They are thus far more loosely set than is customary. The
second segment is a downwardly directed point of hard chitin, whose
work is assisted by spines at the distal end of the first segment. These
appendages therefore closely resemble the chelicerae of spiders, but
they have no poison glands.
The pedipalpi are powerful appendages, composed of the usual six
segments (Fig. 40). Their characteristic in Uropygi is the way in which
their coxae meet and are fused together in the middle of the body, and
thus they have no maxillary gnathites, very little freedom of movement
and no masticatory function. But each trochanter has a large semicircular
process on its inner side, armed with several sharp tubercles.
These processes can be pressed upon each other, or they can be opposed
to the femora by bending the coxo-femoral articulation, and are thus
well adapted to crushing the prey. The patella also has a conspicuous
process, the "third apophysis", at its distal end on the inner side, against
which the tibia closes, a second pincer. In some genera this patellar
process is longer in the male than in the female. At the end of this
appendage, the fixed finger, is a process of the tibia, and the movable
finger is formed by fusion of the tarsus and basitarsus.
The legs of the first pair are not used for walking, but are held
FrG. 40. Peclipalp of Thelyphonus. After Graveley. (i) Trochanter; (ii) tibia; (iii)
transtarsus; (iv) tarsus.
stretched out in front as tactile organs. They are composed of seven true
segments, but the tarsus is subdivided into nine parts. In the female
these tarsal segments arc swollen or variously modified. The true ambulatory
limbs have the tarsus divided into three parts, ending in three
claws.
The fusion of the pedipalpal coxae results in the formation of a
buccal cavity in front of the true mouth or opening into the pharynx.
In Uropygi this is formed by the palpal coxae below and at the sides
and by the chelicerae and a small upper lip above.
DISTRIBUTION
U ropygi are purely tropical Arachnida, and are found in two separate
areas in America, the southern states of the USA and the northeastern
portion of South America. A few specimens of two species of the
genus Hypoctonus have been taken in Gambia. They are not regarded
as true African members of the order, but as immigrants that have been
fortuitously introduced during the past century. They probably entered
with the earth surrounding the roots of imported crop plants. U ropygi
are also found in India and southern China, as well as in Malaysia and
Japan (Fig. 41).