Savory - Arachnida 1977

13
The Order Scorpiones
[Scorpionides Latreille, 1817; Scorpiones Hemprich, 1826; Scorpiides
Koch, 1837; Scorpionida Pearse, 1936]
Arachnida size in which the prosoma by an
undivided carapace bearing two median and two to qf lateral
tryes. The opistlwsoma is markedly divisible into a me so soma of seven (or
somites with that are broader than long, and a metasoma of
five quadrate or cylindrical somites, forming the "tail". There is no pedicel.
A telson is in the form of a poison-bearing sting. The chelicerae are
small, of three segments, chelate. The pedipalpi are characteristically large
and powerful, and are of six segments, chelate. The legs are of seven
segments, without sub-articulations, and the tarsi carry two clazcs. The
sternum is triangular or pentagonal. The second opistlzosomatic
bears a pair of combs or pectines. Four pairs of book-lungs open on the
third, fourth, fifth and sixth stemites.
The prosoma of the scorpions is uniformly coven·d with a hard cephalic
shield or carapace, its width equal to or nen greater than its length.
There are no extensive traces of the primitive segmentation. There is a
median furrow in the middle of the carapace, running from behind the
eyes to the posterior where it widens to form a triangular
• depression: this is an uncommon feature among the primitive orders of
Arachnida (Fig. 28).
The median eyes are placed close on a low ocular tubercle
usually some way from the anterior border of the carapace, but genera
occur in which its position is either farther forward or farther back than
the normal. The lateral eyes form groups of two, three, four or fi\·e
small ocelli almost equal in size. A few scorpions are blind. Although
the eyes are outwardly similar they difier in development. The median
eyes are derived from two layers of hypodermis and are therefore