Savory - Arachnida 1977

178 III. PROLES ARACHNES
The family Heterotarbidae contains one genus and one species,
Heterotarbus ovatus. This about 14 mm long, has very small
chelate chelicerae. Its pedipalpi are invisible, save for their trochanters
which separate the first pair of legs. The first legs are long and slender,
the rest short and stout. The opisthosoma consists of ten somites, five
short followed by five long ones. The coxae and chelicerae of this species
place it between the Opiliones and the rest of its own order.
The family Opiliotarbidae, founded by Petrunkevitch in 1949, contains
only the species formerly known as Architarbus elongatus, described
from Braidwood, Illinois, by Scudder in 1890.
The family Architarbidae contains 11 genera and some 20 species.
The genus Geratarbus contains two American species, G lacoei and
G. minutus, which have a small oval sternum and the first pair of coxae
touching each other. The genus Discotarbus consists of one American
species, D. deplanatus, which has a triangular prosoma and a wide
rounded opisthosoma. Its sternum is divided into three areas. The genus
:.\Ietatarbus, which also consists of one American species, Af. triangularis,
resembles the latter, but has an elongated oval abdomen. The only
European genus is Phalangiotarbus, with one species, P. subovalis. It
differs from its American allies in having a straight posterior edge to the
prosoma instead of a procurved margin. In this family the coxae of the
first pair of legs are contiguous throughout their entire length, and hide
the chelicerae completely (Fig. 63). The genus Architarbus has a remarkable
prosoma, pointed at both ends. The anterior margin is drawn
out to a sharp point, almost like a spine. The posterior projection has
23. THE ORDER ARCHITARBI 179
curved sides meeting at a rounded point which somewhat displaces the
anterior somites of the opisthosoma. This part of the body is rounded
and the first somites are very short. This is a relatively large genus, with
both American and European species.
This is the fifth and last order of extinct Arachnida and at this point
it is of some interest to compare them thus:
FAMILIES GEXERA SPECIES
Kustarachnae I 3
Trigonotarbi 5 I3 20
Anthracomarti I 10 16
Haptopoda I I I
Architarbi 3 14 I9
Thus the total number of described species is than 60, and
almost one-third of these belong to Architarbi. Their distribution
included both European and American sites, but little can be deduced
from this since the discoverv of fossil invertebrates is more influenced bv
opportunity than any othe; factor.
'
All families were in existence during the Carboniferous, Trigonotarbi
are also known from the Devonian and only Anthracomarti seem
to have survived into the Permian.
FIG. 63. Architarbus rotunda/us. After Petrunkevitch.