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.