This find indicates that the eyes in Cyphophthalmi are not homologous to the eyes of other harvestmen. A 305-million-year-old fossilized harvestman with two pairs of eyes was reported in 2014. Eyes in Cyphophthalmi, when present, are located laterally, near the ozopores. Most Opiliones, except for Cyphophthalmi, have a single pair of eyes in the middle of the head, oriented sideways. The stomotheca is formed by extensions of the coxae of the pedipalps and the first pair of legs. The feeding apparatus ( stomotheca) differs from most arachnids in that Opiliones can swallow chunks of solid food, not only liquids.
In short-legged species, this may not be obvious. The second pair of legs is longer than the others and function as antennae or feelers. Some of them are divided medially on the surface to form two plates beside each other. In some species, the two posterior abdominal segments are reduced. Some such Opiliones only have this shield in the males. In some highly derived species, the first five abdominal segments are fused into a dorsal shield called the scutum, which in most such species is fused with the carapace. They also have no silk glands and therefore do not build webs. Other differences include the fact that Opiliones have no venom glands in their chelicerae, so pose no danger to humans. 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. As in all Arachnida, the body in the Opiliones has two tagmata, the anterior cephalothorax or prosoma, and the posterior 10-segmented abdomen or opisthosoma.
The Opiliones are known for having exceptionally long legs relative to their body size however, some species are short-legged. Harvestmen (Opiliones sp.) filmed in Hesse, Germany. Harvestmen are also referred to as "shepherd spiders" in reference to how their unusually long legs reminded observers of the ways that some European shepherds used stilts to better observe their wandering flocks from a distance.
Spiders have a distinct abdomen that is separated from the cephalothorax by a constriction, and they have three to four pairs of eyes, usually around the margins of the cephalothorax.Įnglish speakers may colloquially refer to species of Opiliones as "daddy longlegs" or "granddaddy longlegs", but this name is also used for two other distantly related groups of arthropods, the crane flies of the family Tipulidae, and the cellar spiders of the family Pholcidae, most likely because of their similar appearance. They can be easily distinguished from long-legged spiders by their fused body regions and single pair of eyes in the middle of the cephalothorax. Although superficially similar to and often misidentified as spiders (order Araneae), the Opiliones are a distinct order that is not closely related to spiders. Their phylogenetic position within the Arachnida is disputed their closest relatives may be the mites ( Acari) or the Novogenuata (the Scorpiones, Pseudoscorpiones, and Solifugae). These fossils look surprisingly modern, indicating that their basic body shape developed very early on, and, at least in some taxa, has changed little since that time. Well-preserved fossils have been found in the 400-million-year-old Rhynie cherts of Scotland, and 305-million-year-old rocks in France. Representatives of each extant suborder can be found on all continents except Antarctica. The order Opiliones includes five suborders: Cyphophthalmi, Eupnoi, Dyspnoi, Laniatores, and Tetrophthalmi, which were named in 2014.
As of April 2017, over 6,650 species of harvestmen have been discovered worldwide, although the total number of extant species may exceed 10,000. The Opiliones (formerly Phalangida) are an order of arachnids colloquially known as harvestmen, harvesters, or daddy longlegs. Hadrobunus grandis showing its body structure and long legs: one pair of eyes and broadly joined body tagma differentiate it from similar-looking arachnids.
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