Savory - Arachnida 1977

176 Ill. PROLES ARACHNES
madeleyi (Fig. 62). The animal was about 11 mm long. Nine specimens
are known, all from Britain, where it was discovered at Coseley,
Worcestershire. Therefore it was probably a common species, and one
of the curiosities of arachnology is the fact that no specimen has been
found on the Continent, and no other species of the order has occurred
in any other part of the world.
23
The Order Architarbi
[Phalangiotarbi Haase, 1890; Architarbi Petrunkevitch, 1945;
Architarbida Petrunkevitch, 1955]
Carboniferous Arachnida in which the prosoma is covered by an undivided
carapace, having two eyes level with its surface or with an eye-tubercle,
carrying three pairs of eyes. The opisthosoma is of ten or 11 somites;
the first four to six somites are compressed and divided by a median line.
There are usually nine sternites, similarly divided into three by two longitudinal
lines; the first sternite is triangular and lies between the fourth
coxae, the second has two orifices, the last is circular. The sternum is long
and narrow and consists of three or four sternites. The chelicerae are of
three segments and are chelate. The pedipalpi are slender and are of six
segments, their coxae are situated above the coxae of the first legs, their
gnathobasesforming a stomotheca. The legs are of seven segments.
The chief peculiarity of this order is the compression of the anterior
somites ofthe opisthosoma, so that their tergites are reduced to narrow
strips. This shortens the body, a process which is also seen in Opiliones,
where it has gone further. In fact there are several ways in which the
Cyphophthalmi of Opiliones and some of the Acari are similar, but
this is not certain evidence that they have been derived from a common
ancestor. In a class in which, like Arachnida, so many alternative
characters exist there are bound to be a number of purely fortuitous
resemblances with no phylogenetic significance at all.
Architarbi are also remarkable in having a peculiar three-lobed
ocular tubercle which carries three pairs of eyes, as well as in the
division of the sternites into three regions by two longitudinal lines or
furrows. This apparent fragmentation of either tergites or sternites is
found in other extinct orders such as Trigonotarbi, but seems not to
have persisted into recent times.
The order consists of three families.