Savory - Arachnida 1977

218 Ill. PROLES ARACHNES
family, Holotergidae, because the opisthosoma seemed to be covered
with a hard unsegmented shield, showing none of the transverse sutures
characteristic of all the other genera.
CLASSIFICATION
The order has at all times been limited to a single family, at first called
Cryptostemmatoidae or Poliocheridae. The name Cryptostemma
Guerin, 1838, for the type genus is, however, preoccupied by Cryptostemma
Herrich-Schaffer, 1835, for the Hemiptera, and for this reason
Ewing ( 1929) proposed the name Ricinoides for the genus and Ricinoidae
for the family. Ewing gives the following table for the classification.
I (2)
2 (I)
3 (4)
4 (3)
5 (6)
6 (5)
CLASSIFICATION OF THE ORDER RICINULEI
Second coxae subtriangular and not meeting on
middle line
Second coxae broad, plate-like and meeting on
middle line
Opisthosoma divided into tergites: palaeozoic
Opisthosoma uniform: palaeozoic
Last segment of chelicerae opposed by two processes
on penultimate segment: fourth segment
of tarsus 2 longer than fifth
Last segment of chelicerae opposed by one process
on penultimate segment: fourth segment of
tarsus 2 shorter than fifth
5
Poliochera Scudder
Curculioides Buckland
3
Ricinoides Ewing
Cryptocellus Westwood
One of the noteworthy features about Ricinulei is due to an accident
which caused someone somewhere to describe them as "primitive
Arachnida", and this adjective was universally applied to them by every
writer until 1945b, when Millot pointed out how inappropriate it is.
In truth the word primitive seems to impose upon its readers a
passive receptivity which prevents them from ever questioning its
accuracy. This is perhaps because the opinion that a given animal is
primitive gives one a comfortable feeling of security. This at least, one
feels, is where we begin. Where do we go from here? The answer to
which question is that we should try to determine in how many ways the
so-called primitive animal has specializations peculiar to itself.
In fact, Mitchell ( 1972) lists 11 features characteristic of the Ricinulei
and distinguishing them from all other orders. So large a number
argues an early origin and a long period of evolutionary specialization.
The second remarkable fact about Ricinulei is their rarity. The first
living specimen was found in 1838, and by 1931, 93 years later, a total
2 7. THE ORDER RICINULEI
219
of 21 more specimens had been reported. Then, in 1933, came the
extraordinary capture by I. T. Sanderson of 317 specimens of R.
sjostedti in the Cameroons, and the following 20 years added about
40 more specimens, belonging to a dozen species.
Hence at one time it could be said that a probably unique feature of
the Ricinulei was that they were an order well known for over a century,
during which period not only every species but actually every specimen
captured could readily be traced.
Such a statement of rarity can no longer be made. In 1966 my former
pupil]. Pollock took about 150 specimens of R. afzelii in Sierra Leone,
and in Guyana the late G. P. Lampel in 1959 collected over 50
specimens of two new species. More remarkable results, however, followed
the exploration of the Mexican caves by Mitchell and others.
The American genus Cryptocellus had long been less well represented
than Ricinoides, but between 1967 and 1973 specimens of the former
were being found in hundreds. One cave, La Cueva de la Florida,
yielded 1,035 specimens of C. pelae;;:i. In the same years the number of
known species was more than doubled and now approaches 30.
Two features of the Ricinulei combine to make them the most romantic
order of the Arachnida, and might even support a claim to be placed
among the most absorbing orders of the animal kingdom. These are
their discovery in fossil form before a living specimen was found; and
the reputation for extreme rarity, which they retained for more than a
hundred years.
Add to this the unusual number of their anatomical specializations, and
the conclusion is unassailable that the unique Ricinulei are the most
fascinating, the most intriguing and the most challenging members of
the invertebrate world.