Zoogeographical Notes on Different Orders of Arachnida

Abstract

The distribution of some orders of Arachnida is determined by the preferred temperature of their environment (i.e., thermopreferendum). Thermophilic orders (i.e., those that live at high temperatures) include: Schizomida, Amblypygi, Thelyphonida (Uropygi), Opilioacarida, most of the scorpions, Solifugae, Opilions Laniatores, and Cyphophthalmi. Thermophobic orders (i.e., resistant to cold temperatures) include: Araneae, Opiliones Eupnoi, Dyspnoi, and some mites. These thermophobic orders generally live in the Far North of Eurasia and North America, including Greenland and high in the mountains. The distribution of some orders is a result of paleogeographical events, whereas the distribution of other orders can be difficult to explain (e.g., Holothyrida, spiders of suborder Mesothelae, with families found in New Zealand and Chile; Ricinulei, the genera of Amblypygi e.g., Phrynus in Indonesia, Trichodamon in Brazil; the presence of only one genus of Thelyphonida in a restricted area in West Africa). Most of these scattered groups are clearly relics. Similarly, in some groups (Scorpiones, Pseudoscorpiones) the presence of American elements in the Mediterranean subregion is surprising and demands explanation.