These larvae are minute oval creatures with a comparatively short apically fringed caudal prolongation and furnished with two pairs of short two-clawed processes, which may represent the limbs of anthropods and possibly the two pairs of legs found in Acari of the family Eriophyidae.
Other large Arachnids have not been derived from the scorpions directly, but have independently developed from aquatic ancestors, and from one of these independent groups - probably through the harvest-men from the spiders - the Acari have finally resulted.
Other side - tending downwards from the scorpion towards the Acari - are the Pedipalpi, the spiders, the book-scorpions, the harvest-men and the water-mites.
- Holothyrus nitidissimus, one of the Acari; after Thorell.
- The Acari include a number of forms which are of importance and special interest on account of their parasitic habits.
Many Acari are parasitic on marine and freshwater molluscs, and others are found on the feathers of birds and the hair of mammals.
Claus, " Degeneration of the Acari and Classification of Arthropoda," Anzeiger d.
Berlese, "Acari, &c., in Italia reperta " (Padova, 1892); Canestrini, Acarofauna Italiana (Padova, 1885); Canestrini and Kramer, " Demodicidae and Sarcoptidae " in Das Thierreich (Berlin, 1899) Michael, " British Oribatidae," Ray Soc.; Idem, " Oribatidae " in Das Thierreich (Berlin, 1898); Idem, " Progress and Present State of Knowledge of Acari," Journ.
The valleys of Ica, Palpa, San Xavier and Nasca are rich and fertile, though they do not extend to the sea; but between Nasca and Acari there is a desert 60 m.
And comprises the valleys of Acari, Atequipa, Atico, Ocona, Majes or Camana, Quilca, with the interior valley of Arequipa, Tambo, Ilo or Moquegua, Ite or Locumba.
TICKS, the common name for Arachnida belonging to the order Acari, of which they constitute the two families, Ixodidae and Argasidae.
Collectively the Ixodidae and Argasidae may be distinguished from other Acari by the presence of a median probe, armed with recurved teeth, which project forwards beneath the mouth and between the palpi, and of a conspicuous spiracular area above and usually behind the base of the fourth leg on each side.
As compared with the majority of Acari, ticks are of large size, distended female specimens of some of the species measuring half an inch or more in length, while even the newly hatched young can hardly be regarded as microscopical.