Fam. 1. Sarcoptidae.—No tracheae or stigmata. Apical rostrum. Oviparous or ovoviviparous. The seventy genera and 530 odd species of this family are divided into a number of sub-families, of which the principal are the Sarcoptinae, the Analgesinae, and the Tyroglyphinae.
(i.) The Sarcoptinae are the so-called “Itch-mites.” They are minute animals, with bodies transversely wrinkled and legs terminating in suckers or bristles. The genus Sarcoptes, which includes about fifteen species, lives in tunnels which it burrows in the skin of mammals.
(ii.) The Analgesinae are the “Birds’-feather Mites.” The principal genera are Pterolichus (120 species), Pteronyssus (33 species), Analges (23 species), Megninia (42 species), and Alloptes (33 species).
(iii.) The Tyroglyphinae[[369]] have received the popular name of “Cheese-mites,” from the best known example of the group. They are smooth-bodied, soft-skinned white Mites, with legs usually terminating in a single claw, sometimes accompanied by a sucker. They are for the most part carrion-feeders, living upon decaying animal or vegetable matter, but a few are parasitic on mammals, insects, and worms.
There are sixteen genera, including about fifty species. Tyroglyphus siro and T. longior are common Cheese-mites. Other species live in decaying vegetables and food-stuffs. Some of the genus Glycyphagus (G. palmifer, G. plumiger) are very remarkable for the palmate or plumose hairs which decorate their bodies. The remarkable hypopial stage in the development of Tyroglyphus has been mentioned on p. 463. The Tyroglyphinae are the lowest of the free-living Acarine forms.
Sub-Order 3. Metastigmata.
The four families which constitute this sub-order comprise a large number of Mites in which the tracheae open near the articulation of the legs, and consequently in a somewhat posterior situation. The families are Oribatidae, Argasidae, Ixodidae, and Gamasidae.
Fam. 1. Oribatidae.—The Oribatidae or “Beetle-mites” are free-living Acari, with tracheae of which the stigmata are concealed by the articulation of the legs. The cephalothorax is distinctly marked off from the abdomen, and bears dorsally two “pseudo-stigmatic” organs. The rostrum is inserted below the cephalothorax. These Mites gain their popular name from the beetle-like hardness of their integuments. They are oviparous or ovoviviparous. Eyes are always absent.
Fig. [242].—Oribatid Mites. A, Cepheus ocellatus, × 24; B, ventral view of Hoploderma magnum, closed, × 20. (After Michael.)