Savory - Arachnida 1977

164 HI. PROLES ARACIINES
There are still no records of fossil spiders from the southern hemisphere.
CLASSIFICATION
The classification of spiders has always presented the difficulties that
are provided by any large group of animals in which the number of
known species and genera is rapidly increasing, and in which the course
of evolution is so obscure that it can be traced only in outline.
Many systematists have agreed in recognizing three sub-orders, the
first or most primitive of which is the Liphistiomorphae, containing the
Asiatic Liphistiidae. The second sub-order contains the Theraphosomorphae,
previously known as the M ygalomorphae: the character of
these two groups is outlined above. All other spiders were placed in the
third sub-order, Arachnomorphae or Araneomorphae or Gnaphosomorphae.
The breaking up of the second sub-order into eight or nine families
has not proved to be difficult; not so the many families in the third suborder.
It has not proved easy to construct a truly phylogenetic system,
so that schemes proposed have been purely artificial ones, based on
external characteristics, and valuable chiefly because it made easier the
identification of any specimen under examination. This is the practical
value of any system of classifying objects of any sort.
One classification stands out above all the others, that of Petrunkevitch
in 1933, a courageous attempt to include internal structures
among the characteristics used.
As a result of cutting sections of all representative Petrunkevitch
based his first divisions on the number of ostia through which
the heart communicated with the pericardium. There is no doubt that
the basic idea that all the organs of an animal should be considered in
making a natural system of classification is theoretically so sound as to be
beyond criticism; it is equally undoubted that very few practising
systematists have both the time and the skill needed to or to
section all the animals they are asked to name, and as a result Petrunke~
vitch's system has beer: universally admired and simultaneously
neglected.
Other systems have in general been attempts to improve on their
predecessors: all made use of external features easily visible-the
presence or absence of a cribellum, the simplicity or complexity of the
sex organs, tbe existence of two or of three claws on the tarsi-and it
be readily understood that the systems suggested have become ever
more complex.
In the latest system, that of Bonnet ( 1959), in the second volume of his
18. THE ORDER ARANEAE 165
"Bibliographia Araneorum", there is a summary of the characteristics
of its predecessors, criticizes them where criticism is necessary, and adds
that, with the objections now clearly seen, "c'est le fruit mur qui ne
demande qu'a etre cueilli".
The result contains nine taxa above the genus, namely sub-order,
legion, sub-legion, super-cohort, cohort, sub-cohort, super-family,
family and sub-family. It also gives a number of new names to some of
the taxa which do not come under the notice of the International Rules
of Zoological Nomenclature, and which were revised for various
reasons, some of them merely linguistic.
Bonnet's is the most elaborate and detailed classification of spiders as
yet published, and would probably have received universal acceptance
and approval had it not appeared at the end of his encyclopaedic
Bibliographia Araneorum, whose circle of readers could not be a wide
one. In outline it was as follows:
Sub-order Mesothelae
Legion Liphistiomorphae
Sub-order Opisthothelae
Super-legion Orthognatha
Legion Theraphosomorphae
Super-legion Labidognatha
Legion Gnaphosomorphae
Sub-legion Cribellatae
Ecribellatae
Super-cohort Apneumonatae
Cohort Telemoidea
Super-cohort Dipneumonatae
Cohort Sicarioidea
Cohort Argiopoidea
Sub-cohort Trionycha
Sub-cohort Dionycha
2 families
9 families
12 families
3 families
6 families
16 families
12 families
This scheme embraces a total of 60 families, to which several newly
established families may be added. These include the Toxopidae,
Gradungulidae, Textricellidae, Micropholcommatidae and Austrochilidae
from the southern hemisphere; some new families produced by
a splitting of the Sicariidae, and at least seven fossil families from amber.
KEY GIVING PARTIAL SEPARATION OF THE ABOVE GROUPS
Spinnerets in mid-ventral region of opisthosoma
(~fesotheJae)
LIPHISTIOMORPHAE
2 ( 1) Spinnerets at posterior end of opisthosoma
(Opisthothelae) 3
3 ( 4) Chelicerae striking vertically and parallel
(Orthognatha)
THERAPHOSOMORPHAE