Savory - Arachnida 1977

110 11. DE ARACHNIDIS
Araneae, and so support the idea that they show "the spider pattern".
Their general appearance is that of a spider with long legs and no
spinnerets; the shape of the sternum recalls that of the Liphistiidae,
and the sub-pharyngeal part of the nervous system is striking evidence
of this relationship.
The fossil Kustarachnae may claim the last place in this grouping.
They show relationships to both the spiders and the Schizomida, but
they appear to be older than either of these orders, a belief that is
indicated by the deeper start of the line leading to their name.
(4) Ifthe fact that an order which lived in the Carboniferous is now
extinct may be taken to imply a failure to adapt to changed circumstances,
then the Kustarachnae must be followed by other orders
now extinct. Of these the Trigonotarbi, which alone appear in the
Devonian, must take first place, with a deeper originating level. At
that period they were well developed, and so, very possibly, were other
orders whose remains have never been found.
They were not very distant relatives of the Anthracomarti, which
therefore occupy the next place, and bring with them the other member
of Petrunkevitch's Stethostomata, the Haptopoda. This order, in which
the species had two eyes, 11 opisthosomatic somites, three-segmented
chelicerae and sub-segmented tarsi; sufficiently recall the Opiliones to
secure next place for this order.
( 5) In this assemblage the Opiliones must undoubtedly be accompanied
by the Acari, because the notostigmatic mites show such close
relationships with the Cyphophthalmi; and with them must come the
extinct Architarbi. This recalls Petrunkevitch's suggestion that "these
three represent three branches of a single ancestral group".
In this possibly surprising trio there may be found the characteristics
of blindness, a thickened exoskeleton with furrows marking the original
segments, shortened abdomen without a telson, sub-segmentation of the
tarsi, a cryptozoic life with indifference to starvation, colours unusual
in the class, and above all, the existence of nymphs with six legs. This
catalogue forms so good a diagnosis of the Ricinulei that it clearly
points to the inclusion of that order in the next place.
(6) Two orders remain, the Pseudoscorpiones and the Solifugae.
Many systematists have isolated the latter from all the others and put
them in the last place in their classifications, but the realization that the
false scorpions are only superficially like the real scorpions has led to the
recognition of their relations with the Solifugae. To a superficial glance
these two orders are not as similar as are the false and true scorpions,
but other characteristics bring the Solifugae into the true perspective.
Thus, both orders retain clear and complete segmentation of the abdomen,
both lack pedicel, pygidium and telson; in both the pedal coxae
12. TAXONOMY: CLASSIFICATION 111
meet in the middle line, and both haH two-jointed chelicerae. Their
most obvious difference lies in the development of the chelicerae in the
Solifugae and the pedipalpi in the Pseudoscorpioues, but these are
adaptations to their different environments and modes of living. It may
be added, for good measure, that both arc reported to relish bed bugs in
their diet.
The dcndrogram most aptly raises the problem of the writing out of a
classification of Arachnida in normal tabular form, for in doing this a
decision must be made bct\\·ecn two opposing principles.
The simple solution is that presented among the preliminary matter
of this book ( p. xi). The class is divided into four sub-classes, in each of
which the orders are placed in a uniform list, following the succession of
their names in the dcndrogram. The result is a sort of index, com·eying
the minimum of information.
The alternative and less simple solution attempts to suggest the
degrees of similarity and difference between the orders. This can be
done by introducing a number of intermediate taxa between sub-class
and order: in the classification given below these arc called infra-classes,
cohorts and super-orders. If these subsidiary taxa are to be ginn names
some inventive thought is needed, and probably strict adherence to pure
classical accidence is impossible. However, no arachnologist is obliged
or expected to accept either the method or the nomenclature; for the
devices of taxonomy haH always been subject to individual opinions and
the International Code of Zoological ~omcnclature allows complete
freedom of choice above the names of families. \\'ith these resen·ations
in mind, the classification may be written as follows.
CLASS .\R.\CH.\"ID.\
Sub-cla's Scorpionmorphae
Order l Scorpiones
Sub-class Arachnomorphae
Infra-class Palpigradoidea
Order 2 Palpigradi
Infra-class Arachnoidea
Cohort l: ropygaceae
Super-order l: ropygoides
Order 3 Uropygi
Order 4 Schizomida
Cohort ,\ranaceae
Su;Jer-order Aranoides
Order 5 Amblypygi
Order 6 ,\raneae
Super-order Kustarachnoides
Order 7 Kustarachnae