Savory - Arachnida 1977

8 I. PROLEGOMENA
The Linnaean Insecta were exactly the same as the phylum Arthropoda,
as defined in 1845 by C. T. E. von Siebold and H. Stannius, and
they therefore included a number of wingless forms, which were united
in a common order, the Aptera. The true Insecta, with wings and six
legs, were placed by Lamarck in a class Hexapoda, but this name has
not been universally adopted, that of the parent group, Insecta, being
usually retained.
From the Aptera Lamarck extracted several classes, one of which was
"Classe Troisieme-les Arachnides". At that time it contained scorpions,
spiders and mites, together with some excusable intrusions. The
class Arachnida, as here recognized, contains 12 living and five extinct
orders:
ACARI
AMBLYPYGI
tANTHRACOMARTI
ARANEAE
tARCHITARBI
CYPHOPHTHALMI
tHAPTOPODA
t K USTARACHNAE
OPILIONES
PALPIGRADI
PSE UDOSCORPIONES
RICINULEI
t Extinct orders
SCHIZO MID A
SCORPIONES
SOLIFUGAE
tTRIGONOTARBI
UROPYGI
The order named Pedipalpi by Latreille was clearly heterogeneous.
It was divided by Millot in 1942 into three orders: Phrynides, Thelyphonides
and Tartarides, and independently in 1945 by Petrunkevitch
into the order Phrynichida, Thelyphonida and Schizomida. This
introduction of new names for groups which already had familiar names
in their status as sub-orders was a needless complication, and later
writers have wisely used the older names Amblypygi and Uropygi.
An order named Poecilophysida was founded in 1876 by Pickard­
Cambridge on several examples of primitive stomatostigmatic mites
from Kerguelen's Land: they had been placed by Thorell in 1871 in the
genus Rhagidia.
For readers who may be unfamiliar with some of these Arachnida, a
short survey of the living orders will form a helpful introduction to the
now well-established science of arachnology.
Scorpiones
Scorpions: formidable arachnids, perhaps among the first animals to
leave the water and live on the land. Since the dawn of civilization,
scorpions, conspicuous with their large pincers and poison-sting, have
been feared by man; they have appeared in myths and have been
granted a celestial place in the Zodiac.
Palpigradi
Micro whip-scorpions: diminutive arachnids, leading hidden lives in
2. THE CLASS ARACHNIDA 9
warm countries and deserving, because of their very primitive
structure, more attention than they usually obtain.
Uropygi
Whip-scorpions: fiat-bodied arachnids with a long whip-like telson,
forming a tropical order now beginning to be better appreciated and
more carefully studied.
Schizomida
A small group, related to the above, about which we are not learning
very much.
Amblypygi
Tailless whip-scorpions: more fiat-bodied arachnids, whose whips are
not telsons, but very long and thin first legs. Another order that is
beginning to come to the fore.
Araneae
Spiders: dominant arachnids, known to all men as the spinners of silk
threads that are often used to make elaborate, ingenious and beautiful
webs. There are many species, showing a wide range in structure and
habits.
Cyphophthalmi
Primith·e arachnids: until now included with the harvestmen, to which
they are ancestrally related.
Opiliones
Harvestmen: ludicrous arachnids with two eyes perched on a small
body, often bizarre in form, and supported by legs too long for convenience
and somewhat insecurely attached. Recognized by most people as
clearly different from spiders, there are a score or so of species in Britain,
several of which are commonly to be seen in woods and gardens in the
autumn.
Acari
Mites and ticks: small arachnids, some of them aquatic and some
parasitic. They include the only arachnids of much economic importance
and the only ones studied by economic zoologists. The order is less
homogeneous than any other and has sometimes been placed in a separate
class.
Ricinulei
Mysterious arachnids: scattered over parts of the tropical belt, and at