You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
184 Ill. PROLES ARACHNES<br />
24. THE ORDER OPILIONES 185<br />
FIG. 68. Phalangiurn, ventral aspect. After Roewer.<br />
FIG. 67. Legs ofOpiliones. After Kaestner. (i) Tarsus of Opilio parietinus; (ii) whole !eg<br />
of Nemasloma bimaculatum.<br />
The lower surface of the prosoma is formed from the labium, sternum<br />
and the coxae of the legs (Figs 68 and 69). The labium, as mentioned<br />
above, may be regarded as one of the mouth parts. It is probably homologous<br />
with the corresponding labium of Araneae and represents the<br />
sternite of one of the original somites. Behind it is the sternum proper, a<br />
single plate. In Laniatores it is long and narrow, reaching as far back as<br />
the fourth coxae. In Palpatores it is always short; sometimes it is continuous<br />
with the labial portion and sometimes with the genital plates<br />
behind it, but it is often largely out of sight, hidden below the coxae.<br />
The coxae are sometimes all immovable and sometimes all movable in<br />
Palpatores; in Laniatores the three posterior pairs are immovable, the<br />
fourth pair coalescing with the opisthosoma, while the first pair can be<br />
rotated, moving their maxillary lobes towards or away from the<br />
mandibles.<br />
The opisthosoma is usually so closely united to the prosoma that the<br />
distinction between the two parts is not obvious. Its precise structure is<br />
not easily elucidated without the comparison of many forms, since segments<br />
are often fused together or are missing, and also because the<br />
tergites and. sternites of the same segment are not always placed opposite<br />
each ~ther m the lateral aspect of the adult. The shape of the opisthosoma<br />
IS usually oval or globular, but it is flattened in Trogulidae. It is<br />
covered with a fairly hard exoskeleton often decorated with spines. In<br />
European species these are small and usually amount to no more than<br />
rows of points indicating segments, but in many tropical forms as in the<br />
Gonyleptidae, there are more elaborate developments. '<br />
In most Palpatores, nine tergites and nine sternites can be recognized,<br />
followed by the operculum anale, a small circular plate pierced by a<br />
transverse or round anus. This operculum is regarded as the tergite<br />
only of the tenth somite. Hence in these two sub-families there are ten<br />
FIG. 69. Hornalenotus, ventral aspect, expanded.
Change language