Remarks on the Opiliones.—These include the harvest-men, sometimes called also daddy-long-legs, with round undivided bodies and very long, easily-detached legs. The intromittent organs of the male are remarkable for their complexity and elaboration. The confluence of the regions of the body and the dislocation of apertures from their typical position are results of degeneration. The Opiliones seem to lead on from the Spiders to the Mites. Reference to literature (39).
 | Fig. 77.—Stylocellussumatranus, one of theOpiliones; after Thorell.Enlarged. |
A, Dorsal view; I to VI, the six prosomatic appendages. B, Ventral view of the prosoma and of the firstsomite of the opisthosoma, with the appendagesI to VI cut off at the base; a, trachealstigma; mx, maxillary processes of the coxae ofthe 3rd pair of appendages; g, genital aperture. C, Ventral surface of the prosoma and opisthosoma;a, tracheal stigma; b, last somite. D, Lateral view of the 1st and 2nd pair of appendages. E, Lateral view of the whole body and two 1st appendages, showingthe fusion of the dorsal elements of the prosoma into a singleplate, and of those of the opisthosoma into an imperfectly segmentedplate continuous with that of the prosoma. |
Apparently related to the Opiliones are two extinct groups, the Anthracomarti and Phalangiotarbi, which are not known to have survived the Carboniferous period. In the Anthracomarti the opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment. The carapace of the prosoma was unsegmented and often bore a pair of eyes. The appendages of the 2nd pair were slender and pediform; those of the 3rd, 4th, 5th and 6th pairs were similar in form and ambulatory in function with their basal segments arranged round a sternal area as in the order Araneae. The best-known genera were Anthracomartus and Eophognus.
In the Phalangiotarbi the appendages resembled those of the Anthracomarti, except that the basal segments of the last four pairs were usually approximated in the middle line leaving a long and narrow sternal area between; and the carapace of the prosoma was unsegmented. The prosoma and opisthosoma were broadly confluent and probably immovably welded together. The opisthosoma consisted of eight or nine segments, whereof the anterior five or six were very short in the dorsal region, and the posterior three exceptionally large with the anal orifice terminal.
Several genera have been established, the best-characterized being Geraphognus and Architarbus.
Order 9. Rhynchostomi = Acari (see fig. 78).—Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features:—The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stigmata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.
Sub-order a. Notostigmata.—Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four of these furnished with a single pair of dorsally-placed spiracles or tracheal stigmata.
Family—Opilioacaridae (Opilioacarus).
Sub-order b. Cryptostigmata.—Integument hard, strengthened by a continuously chitinized dorsal and ventral sclerite. Tracheae typically opening by stigmata situated in the articular sockets (acetabula) of the 3rd, 4th, 5th and 6th pairs of appendages.
Family—Oribatidae (Oribata, Nothrus, Hoplophora).