Harvestman

Opiliones (formerly Phalangida) are an order of arachnids commonly known as harvestmen. As of December 2011, over 6,500 species of harvestmen have been discovered worldwide,[1] although the real number of extant species may exceed 10,000.[2] The order Opiliones includes four suborders: Cyphophthalmi, Eupnoi, Dyspnoi, and Laniatores. Well-preserved fossils have been found in the 400-million-year-old Rhynie cherts of Scotland, which look surprisingly modern, indicating that the basic structure of the harvestmen has not changed much since then. Phylogenetic position is disputed: their closest relatives may be the mites (Acari) or the Novogenuata (the Scorpiones, Pseudoscorpiones and Solifugae).[3]
Although they belong to the class Arachnida, harvestmen are in the order Opiliones; therefore they are not spiders, which are members of the order Araneae.
In some places, Opiliones are known by the name "daddy longlegs" or "granddaddy longlegs", but this name is also used for two other unrelated arthropods: the crane fly (Tipulidae) and the cellar spider (Pholcidae).