Mites
Definition
Mites are the most diverse of all arachnids, and among the oldest of all terrestrial animals. Fossils date mites from the early Devonian, nearly 400 million years ago. [1] Belonging to the class Archnida, the term "mite" refers to the several groups in the subclass Acari, but it is not a clade, and excludes the ticks. Mites and ticks are similarly characterized by their bodies being divided into two parts, named the cephalothorax and opisthosoma. The three major lineages of mites are recognized as Opilioacariformes, Acariformes and Parasitiformes. 45,000 species of mites have been described, which is believed to be only small 5% of the number of species estimated to be alive today. [3]
Characteristics
The Acari can be defined by the following characteristics [3]:
- Hexapod prelarva (lost in Parasitiformes and many derived Acariformes)
- Hexapod larval stage
- Three octopod nymphal stages (variously abbreviated in derived taxa)
- Gnathosoma delimited by a circumcapitular suture
- Palpcoxal endites fused medially forming a hypostome
- Hypostome with rutella or corniculi (lost in many derived Acariformes)
- Loss of external evidence of opisthosomal segmentation, i.e. without tergites or sternites
- Ingestion of particulate food (lost in many derived taxa)