Editing Opiliones (section)

== Description ==
{{Main|Opiliones anatomy}}
[[File:Pseudo-araña nocturna (opilion).jpg|thumb|left|Chilean harvestman (''[[Pachyloidellus goliath]]'')]]
[[File:Harvester body close up.jpg|thumb|left|North European harvestman (''[[Leiobunum rotundum]]'') body]]
[[File:We-2012-09-09.ogv|thumb|250px|Harvestmen (Opiliones sp.) filmed in Hesse, Germany]]
The Opiliones are known for having exceptionally long legs relative to their body size; however, some species are short-legged. As in all Arachnida, the body in the Opiliones has two [[Tagma (biology)|tagmata]], the [[Anatomical terms of location|anterior]] [[cephalothorax]] or [[prosoma]], and the [[Anatomical terms of location|posterior]] 10-segmented [[abdomen]] or [[opisthosoma]]. The most easily discernible difference between harvestmen and spiders is that in harvestmen, the connection between the cephalothorax and abdomen is broad, so that the body appears to be a single [[oval]] structure. Other differences include the fact that Opiliones have no [[Spider Bite|venom]] glands in their [[chelicerae]] and thus pose no danger to humans.

They also have no silk glands and therefore do not build webs. In some highly derived species, the first five abdominal segments are fused into a [[Anatomical terms of location|dorsal]] shield called the [[scute|scutum]], which in most such species is fused with the [[carapace]]. Some such Opiliones only have this shield in the males. In some species, the two posterior abdominal segments are reduced. Some of them are divided [[Anatomical terms of location|medially]] on the surface to form two plates beside each other. The second pair of legs is longer than the others and function as [[Antenna (biology)|antennae]] or feelers. In short-legged species, this may not be obvious.

The feeding apparatus ([[stomotheca]]) differs from most arachnids in that Opiliones can swallow chunks of solid food, not only liquids. The stomotheca is formed by extensions of the coxae of the [[pedipalp]]s and the first pair of legs.

Most Opiliones, except for Cyphophthalmi, have long been thought to have a single pair of camera-type eyes in the middle of the head, oriented sideways. Eyes in Cyphophthalmi, when present, are located laterally, near the ozopores. A 305-million-year-old fossilized harvestman with two pairs of eyes was reported in 2014. This find suggested that the eyes in Cyphophthalmi are not homologous to the eyes of other harvestmen.<ref>{{Cite web |last=Blaszczak-Boxe |first=Agata |date=2014-04-10 |title=4-Eyed Daddy Longlegs Helps Explain Arachnid Evolution (Video) |url=https://www.livescience.com/44742-daddy-longlegs-fossil.html |access-date=2023-07-16 |website=livescience.com |language=en}}</ref><ref>{{cite journal |title=A Paleozoic Stem Group to Mite Harvestmen Revealed through Integration of Phylogenetics and Development |doi=10.1016/j.cub.2014.03.039 |pmid=24726154 |volume=24 |issue=9 |journal=Curr Biol |pages=1017–23 | last1 = Garwood | first1 = RJ | last2 = Sharma | first2 = PP | last3 = Dunlop | first3 = JA | last4 = Giribet | first4 = G|year=2014 |doi-access=free |bibcode=2014CBio...24.1017G }}</ref> Many cave-adapted species are eyeless, such as the Brazilian ''[[Caecobunus termitarum]]'' ([[Grassatores]]) from [[termite]] nests, ''[[Giupponia chagasi]]'' ([[Gonyleptidae]]) from caves, most species of Cyphophthalmi, and all species of the [[Guasiniidae]].<ref>{{cite journal |first1=Ricardo |last1=Pinto-da-Rocha |first2=Adriano B. |last2=Kury |year=2003 |title=Third species of Guasiniidae (Opiliones, Laniatores) with comments on familial relationships |journal=[[Journal of Arachnology]] |volume=31 |issue=3 |pages=394–399 |url=http://www.americanarachnology.org/JoA_free/JoA_v31_n3/arac-031-03-0394.pdf |doi=10.1636/H02-59 |s2cid=85918640 |access-date=2007-08-27 |archive-date=2016-03-28 |archive-url=https://web.archive.org/web/20160328120657/http://www.americanarachnology.org/JoA_free/JoA_v31_n3/arac-031-03-0394.pdf |url-status=dead }}</ref> However, recent work studying the embryonic development of the species ''[[Phalangium opilio]]'' and some Laniatores revealed that harvestman in addition to a pair of median eyes also have two sets of vestigial eyes: one median pair (homologous to those of [[horseshoe crab]]s and [[sea spider]]s), and one lateral pair (homologous to facetted eyes of horseshoe crabs and insects).<ref name=":17">{{Cite journal |last1=Gainett |first1=Guilherme |last2=Klementz |first2=Benjamin C. |last3=Blaszczyk |first3=Pola |last4=Setton |first4=Emily V.W. |last5=Murayama |first5=Gabriel P. |last6=Willemart |first6=Rodrigo |last7=Gavish-Regev |first7=Efrat |last8=Sharma |first8=Prashant P. |date=February 2024 |title=Vestigial organs alter fossil placements in an ancient group of terrestrial chelicerates |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982224001532 |journal=Current Biology |volume=34 |issue=6 |pages=1258–1270.e5 |language=en |doi=10.1016/j.cub.2024.02.011|pmid=38401545 }}</ref> This discovery suggests that the neuroanatomy of harvestmen is more primitive than derived arachnid groups, like spiders and scorpions. It also showed that the four-eyed fossil harvestman previously discovered is most likely a member of the suborder [[Eupnoi]] (true daddy-longlegs).<ref name=":17" />

[[File:Harvestman macro.jpg|thumb|right|A harvestman (a male ''Phalangium opilio''), showing the almost fused arrangement of abdomen and cephalothorax that distinguishes these arachnids from [[spider]]s]]
Harvestmen have a pair of prosomatic defensive [[scent gland]]s ([[ozopore]]s) that secrete a peculiar-smelling fluid when disturbed. In some species, the fluid contains noxious [[1,4-Benzoquinone|quinones]]. They do not have [[book lungs]], and breathe through [[invertebrate trachea|tracheae]]. A pair of [[Spiracle (arthropods)|spiracles]] is located between the base of the fourth pair of legs and the abdomen, with one opening on each side. In more active species, spiracles are also found upon the [[tibia]] of the legs. They have a [[gonopore]] on the ventral cephalothorax, and the [[animal sexual behavior|copulation]] is direct as [[Opiliones penis|male Opiliones have a penis]], unlike other arachnids. All species lay [[Egg (biology)|eggs]].

Typical body length does not exceed {{convert|7|mm|abbr=on}}, and some species are smaller than 1&nbsp;mm, although the largest known species, ''[[Trogulus torosus]]'' ([[Trogulidae]]), grows as long as {{convert|22|mm|abbr=on}}.<ref name=pinto/> The leg span of many species is much greater than the body length and sometimes exceeds {{convert|160|mm|abbr=on}} and to {{convert|340|mm|abbr=on}} in Southeast Asia.<ref>{{Cite web |url=http://www.senckenberg.de/root/index.php?page_id=5210&year=2012&action=press&id=2480 |title=SENCKENBERG world of biodiversity &#124; About us &#124; Communications &#124; Newsroom |access-date=2015-05-29 |archive-url=https://web.archive.org/web/20151119111459/http://www.senckenberg.de/root/index.php?page_id=5210&year=2012&action=press&id=2480 |archive-date=2015-11-19 |url-status=dead }}</ref> Most species live for a year.