Savory - Arachnida 1977

172 Ill. PROLES ARACHNES
number of book-lungs varies from two to four or even eight, as in the
family Eophrynidae. It is this repeated instability in such basic structural
formations that suggested the name Soluta for the sub-class.
Evidence of relationship between arachnid orders is often sought by
examining the coxo-sternal arrangement, which plays so important a
part in feeding. In the Trigonotarbi there is a labium anterior to the
sternum, which is edged on each side by five coxae, a typical pattern
shown also by the Araneae, but lacking the gnathobases of the pedipalpi.
And a detail that also recalls some spiders of the family Araneidae is the
existence of sharply pointed tubercles on the hind edge of the abdomen.
Trigonotarbi are also related to the Anthracomarti (Chapter 21), but
can be distinguished from that order by the possession of three, not
five, parts to the opisthosomatic tergites.
The general character of the order may be summarized by the statement
that to a number of peculiarities of their own they add an almost
equal number of resemblances to several other orders, a condition that
is to be found elsewhere in the Arachnida and may be associated with a
long period of evolution through the geological ages.
21
The Order Anthracomarti
[ Anthracomarti Karsch, 1882; Anthracomartida Petrunkevitch,
1955]
Carboniferous and Permian Arachnida, in which the prosoma is covered by
an undivided carapace, on which there are no ryes. The sternum is long and
narrow, and there is no pedicel. The opisthosoma is of ten somites, completely
represented by ten tergites and ten sternites; the first tergite may be connected
to the carapace, the second and third are fwed together. Tergites 2 to 9 are
divided into .five plates by four longitudinal lines, and the corresponding
sternites are divided into three plates by two lines. The chelicerae are of
three segments, the third being a retrovert fang. The pedipalpi are of six
segments. The legs are of seven segments, with two claws and an onychium.
This order consists of a single family only, the Anthracomartidae, of
11 genera and fewer than 20 species, described from North America,
Belgium, Britain, Czechoslovakia and Germany (Fig. 61). It is clear
that in their day they were a fairly specialized type, for the mouth has
moved a long way back from its primitive apical position. This may
have necessitated a peculiar diet or a peculiar method offeeding.
The division of the tergites into five portions is most unusual, and it is
difficult to imagine how such a condition came into existence, or what
advantages it brought, save that a swelling of the abdomen after a
large meal would have been made easier. The family seems, however, to
have reached an advanced condition and one of comparative stability,
so that no more than minor changes, resulting in the appearance of new
genera, were possible.
An unusual feature was the possession of three pairs of book-lungs,
opening on abdominal somites 2, 3 and 4.
The two small orders Haptopoda and Anthracomarti were placed
together by Petrunkevitch in 1949 in a sub-class which he named
Stethostomata. Their common feature, which distinguishes them from