Opiliones

From Freepedia

(Redirected from Harvestman)
Opiliones
Image:Harvestman - phalangium opilio.JPG
Harvestman
Scientific classification
Kingdom:Animalia
Phylum:Arthropoda
Class:Arachnida
Order:Opiliones
Sundevall, 1833

The Phalangids (legacy name) or Opiliones (better known as "harvestmen") are eight-legged invertebrate animals belonging to the order Opiliones in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. As of 2000, over 5,000 species of Phalangids have been described worldwide. The order Opiliones can be divided in three families: Nemastomatidae, Phalangiidae and Trogulidae.

The name "daddy longlegs" can also refer to two other unrelated arthropods: the crane fly (Tipulidae) and the cellar spider (Pholcidae).

Contents

Physical description

These harmless arachnids are known for their exceptionally long walking legs, compared to body size. The difference between harvestmen and spiders is that in harvestmen the two main body sections (the prosoma and opisthosoma) are nearly joined, so that they appear to be one oval structure. They have two eyes in the middle of their heads, oriented sideways. They have scent glands that secrete a peculiar smelling fluid when disturbed. Harvestmen do not have silk glands and most do not possess poison glands. Those that do have venom pose absolutely no danger to humans (see below).

The legs continue to twitch after they are detached. This is because there are pacemakers located in the ends of the first long segment (femur) of their legs. These pacemakers send signals via the nerves to the muscles to extend the leg and then the leg relaxes between signals. While some Opiliones legs will twitch for a minute, other kinds have been recorded to twitch for up to an hour. The twitching has been hypothesized as a means to keep the attention of a predator while the Opiliones escapes.

Most species live for a year.

Behavior

Many species are omnivorous, eating primarily small insects and all kinds of plant material and fungi; some are scavengers of the decays of any dead animal, bird dung and other fecal material. Mating involves direct copulation, rather than the deposition of a spermatophore. They are mostly nocturnal.

Endangered status

Some troglobitic Opiliones are endangered if their home caves are in or near cities where pollution and development of the land can alter the cave habitat while others are threatened by the invasion of fireants.

All troglobitic species (of all animal taxa) are considered to be at least threatened in Brasil. Thus far, the only Opiliones on a red list for the state of São Paulo is Pachylospeleus strinatii from caves.

Several Opiliones in Argentina appear to be "vulnerable", if not endangered. These include Pachyloidellus fulvigranulatus, which is found only on top of Cerro Uritorco, the highest peak in the Sierras Chicas chain (provincia de Cordoba) and Pachyloides borellii is in rainforest patches in NW Argentina which are in an area being dramatically destroyed by humans. The cave living Picunchenops spelaeus is apparently endangered through human action. So far no harvestman has been included in any kind of a Red List in Argentina and therefore they receive no protection.

Maiorerus randoi has only been found in one cave in the Canary Islands. It is included in the "Catálogo Nacional de especies amenazadas" (National catalog of threatened species) from the Spanish government.

Texella reddelli and Texella reyesi are listed as endangered species in the U.S.A. Both are from caves in central Texas. Texella cokendolpheri from a cave in central Texas and Calicina minor, Microcina edgewoodensis, Microcina homi, Microcina jungi, Microcina leei, Microcina lumi, and Microcina tiburona from around springs and other restrictive habitats of central California are being considered for listing as endangered species, but as yet receive no protection.

A poisonous myth

There is an urban legend claiming that the daddy longlegs is the most poisonous spider in the world, only its fangs are too small to bite a human, and is thus not actually dangerous. This is untrue on several counts. First, of course, phalangids are not spiders. Many species don't have any poison glands at all. Of those that do, the venom appears to be far less toxic than that of a black widow spider. The size of the fangs varies by species, of course, but even those with relatively long fangs do not bite humans (or other large creatures). The urban legend is probably due to confusion with the Daddy long-legs spider, which can indeed bite and is indeed poisonous, but not dangerously so. More can be read on the debunking of this myth on the Daddy long-legs spider page.

Other names

Retrieved from "http://en.freepedia.org/Opiliones.html"


Views
Personal tools
In other languages
Similar Links