Savory - Arachnida 1977

228 III. PROLES ARACHNES
and tarsus ( telotarsus) fuse, forming a compound miotarsus, and sometimes
the two parts of the femur are united. In the Heterosphyronida
the forelegs have miotarsi and the hind legs have separate metatarsi and
tarsi. In the Diplosphyronida all the metatarsi and tarsi are separate and
in the :\Ionosphyronida all have miotarsi.
The pretarsus consists of two claws and a membranous arolium
between them. The latter is a short sucking pad, which enables the
false scorpion to climb perpendicularly and to walk or rest on the
underside of smooth horizontal surfaces. The tarsal claws are not
toothed. In the forelegs of the males of most Cheliferidae the anterior
claw is distorted and is slenderer than its fellow. The tip of the miotarsus
is often produced into a distinct spine, which is used in mating to open
the female genital operculum and assist the entry of the spermatophore.
The mouth parts of pseudoscorpions lie between the maxillae or
gnathobases of the pedipalpi. The mouth itself is an aperture at the end
of a tube or rostrum formed from dorsal and ventral projections. The
latter, the labium or lophognath, is convex or crested dorsally, and is
immovable. The upper lip, epipharynx or taphrognath, fits over the
lower. By a slight upward movement of the taphrognath, the tube which
they form can be enlarged, thus exerting a slight sucking effect. The
true mouth, however, does not directly touch the food. The coxae of the
pedipalpi enclose the rostrum in a trough-like chamber. Within this
the laminae superiores and laminae inferiores lie closely below the
rostrum, forming a compound tube which touches the prey in feeding
and conducts the juices to the mouth. In the rostrum is an internal
expansion forming a pharyngeal pump similar to, but not homologous
with, the sucking stomach of spiders.
Weygoldt (1972) has described the action of the effective muscle,
which in a Chelifer made 160 vibrations per minute. At intervals,
peristalsis could be seen, forcing the food onwards from the mesenteron.
Indigestible particles were ejected between the palpal coxae, which
were then cleaned by rubbing them on the ground.
The ventral surface of the prosoma (Fig. 98) of pseudoscorpions is
never protected by a large sternum, though a vestige may be found in
certain species. This region is generally composed of the coxae of the
legs and pedipalpi, which touch each other and meet in the middle line.
However, in certain Chthonioidea a chitinous tubercle or platelet
bearing one or two setae is found between the third and fourth coxae.
This is a vestige of the true sternum. A secondary sternum is found in
Garypidae, a mere membranization between the fourth coxae, and
there is a larger secondary sternum in the small family Sternophoridae.
The coxae extend further back than the carapace, and as a result the
ventral surface of the first opisthosomatic segment is reduced.
28. THE ORDER PSEUDOSCORPIONES 229
FIG. 98. Pseudoscorpion. Species Chelifer cancroides, ventral aspect.
The opisthosoma, more or less oval in form, is always broadly
attached to the prosoma. It is fully segmented, with 12 tergites and ten
sternites. The first sternite is either missing or fused with the second,
which, with the third, forms the genital opercula. These enclose the
genital chamber, which opens in the constant place on the second segment.
The terminal somite is reduced to form the anal tubercle.
Tracheae open on the third and fourth sternites.
These hard plates of the opisthosoma are united by an extensible
membrane. Since the abdomen contains the digestive and reproductive
organs, whose bulk is liable to change, the size of the opisthosoma varies
a good deal according to season and circumstances. In many genera the
tergites are medially divided into two parts.
The male organs within the second and third somites are an amazingly
complex invagination of these two sternites. The slit leads to a
uterus masculinus externus, and thence to a uterus masculinus internus.