Opiliones
Harvestmen are eight-legged arachnids. Even though they belong to the arachnid class, harvestmen are not spiders. They are in the order Opiliones or Phalangids.
| Opiliones Temporal range: Devonian – Recent | |
|---|---|
 | |
| Hadrobunus grandis | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Subclass: | Dromopoda |
| Order: | Opiliones Sundevall 1833 |
| Diversity | |
| 4 suborders, > 6,400 species | |
More than 6,400 species of harvestmen have been discovered, although the real number of extant species may be more than 10,000.[1] Well-preserved fossils have been found in the 400-million year old Rhynie cherts of Scotland. The samples found look surprisingly modern. Apparently, the basic structure of the harvestmen has not changed much since then.
In some places, harvestmen are known by the name "daddy longlegs", but this name is also used for two other unrelated arthropods: the crane fly (Tipulidae) and the cellar spider (Pholcidae).
Many species are omnivores, they eat anything they can find. Most of the time this is small insects, and some plants and fungi. Some are scavengers.
Harvestmen are not dangerous to humans. None of the described species have poison glands. They are not "true" spiders even though they look like spiders in many ways. For example, harvestmen have no venom or silk glands; spiders have these.
Anatomy
These arachnids have exceptionally long walking legs, compared to body size, although there are also short-legged species. In harvestmen the two main body sections (the abdomen and cephalothorax) are broadly joined, so that they appear to be one oval structure. They also have no venom or silk glands, unlike true spiders. In more advanced species, the first five abdominal segments are often fused into a dorsal shield called the scutum, which is normally fused with the carapace. In some species, this shield is only present in males. The second pair of legs is longer than the others and works as antennae. This can be hard to see in short-legged species.
The feeding apparatus (Stomotheca) differs from other arachnids as they are able to eat their food in chunks, without needing to liquify it. Most species have a single pair of eyes in the middle of their heads, oriented horizontally. However, there are some eyeless species.
Further reading
- Joel Hallan's Biology Catalog (2005)
- Pinto-da-Rocha R. Machado G. & Giribet G. eds. 2007. Harvestmen – the biology of Opiliones. Harvard University Press ISBN 0-674-02343-9
- Pinto-da-Rocha R. & Kury A.B. 2003. Third species of Guasiniidae (Opiliones, Laniatores) with comments on familial relationships. Journal of Arachnology 31: 394-399. PDF Archived 2016-03-28 at the Wayback Machine
- Shultz, Jeffrey W. 1998. Phylogeny of Opiliones (Arachnida): an assessment of the "Cyphopalpatores" concept. Journal of Arachnology 26: 257-272. PDF Archived 2008-12-16 at the Wayback Machine
Other websites
- Harvestman: Order Opiliones Diagnostic photographs and information on North American harvestmen
- Harvestman: Order Opiliones Diagnostic photographs and information on European harvestmen
- University of Aberdeen: The Rhynie Chert Harvestmen (fossils)
- National Museum page Classification of Opiliones Archived 2020-11-12 at the Wayback Machine A synoptic taxonomic arrangement of the order Opiliones, down to family-group level, including some photos of the families
References
- Pinto-da-Rocha R. Machado G. & Giribet G. eds. 2007. Harvestmen – The biology of Opiliones. Harvard University Press ISBN 0-674-02343-9