Opiliones
Opiliones Early | |
---|---|
Hadrobunus grandis showing its body structure and long legs: one pair of eyes and broadly joined body tagma differentiate it from similar-looking arachnids. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Subphylum: | Chelicerata |
Class: | Arachnida |
Order: | Opiliones Sundevall, 1833 |
Suborders | |
Diversity | |
5 suborders, > 6,650 species |
The Opiliones (formerly Phalangida) are an
Representatives of each extant suborder can be found on all continents except Antarctica.
Well-preserved fossils have been found in the 400-million-year-old Rhynie cherts of Scotland, and 305-million-year-old rocks in France. These fossils look surprisingly modern, indicating that their basic body shape developed very early on,[4] and, at least in some taxa, has changed little since that time.
Their
English 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
Description
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
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 dorsal shield called the 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 medially on the surface to form two plates beside each other. The second pair of legs is longer than the others and function as 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 pedipalps 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.
Harvestmen have a pair of prosomatic defensive
Typical body length does not exceed 7 mm (0.28 in), and some species are smaller than 1 mm, although the largest known species, Trogulus torosus (Trogulidae), grows as long as 22 mm (0.87 in).[2] The leg span of many species is much greater than the body length and sometimes exceeds 160 mm (6.3 in) and to 340 mm (13 in) in Southeast Asia.[12] Most species live for a year.
Behavior
Many species are
Although parthenogenetic species do occur, most harvestmen reproduce sexually. Except from small fossorial species in the suborder Cyphophthalmi, where the males deposit a spermatophore, mating involves direct copulation. The females store the sperm, which is aflagellate and immobile, at the tip of her ovipositor. The eggs are fertilized during oviposition.[13] The males of some species offer a secretion (nuptial gift) from their chelicerae to the female before copulation. Sometimes, the male guards the female after copulation, and in many species, the males defend territories. In some species, males also exhibit post-copulatory behavior in which the male specifically seeks out and shakes the female's sensory leg. This is believed to entice the female into mating a second time.[14]
The female lays her eggs shortly after mating to several months later. Some species build nests for this purpose. A unique feature of harvestmen is that some species practice parental care, in which the male is solely responsible for guarding the eggs resulting from multiple partners, often against
Most species are
Many species of harvestmen easily tolerate members of their own species, with aggregations of many individuals often found at protected sites near water. These aggregations may number 200 individuals in the Laniatores, and more than 70,000 in certain Eupnoi. Gregarious behavior is likely a strategy against climatic odds, but also against predators, combining the effect of scent secretions, and reducing the probability of any particular individual being eaten.[2]
Harvestmen clean their legs after eating by drawing each leg in turn through their jaws.
Antipredator defences
Predators of harvestmen include a variety of animals, including some mammals,[18][19] amphibians, and other arachnids like spiders[20][21] and scorpions.[22] Opiliones display a variety of primary and secondary defences against predation,[23] ranging from morphological traits such as body armour to behavioral responses to chemical secretions.[24][25] Some of these defences have been attributed and restricted to specific groups of harvestmen.[26]
Primary defences
Primary defences help the harvestmen avoid encountering a potential predator and include crypsis, aposematism, and mimicry.
Crypsis
Particular patterns or colour markings on harvestmen's bodies can reduce detection by disrupting the animals' outlines or providing camouflage. Markings on legs can cause an interruption of the leg outline and loss of leg proportion recognition.
Aposematism and mimicry
Some harvestmen have elaborate and brightly coloured patterns or appendages which contrast with the body colouration, potentially serving as an aposematic warning to potential predators.[26][33][34] This mechanism is thought to be commonly used during daylight, when they could be easily seen by any predators.
Other harvestmen may exhibit mimicry to resemble other species' appearances. Some Gonyleptidae individuals that produce translucid secretions have orange markings on their carapaces. This may have an aposematic role by mimicking the colouration of glandular emissions of two other quinone-producing species.[33] Mimicry (Müllerian mimicry) occurring between Brazilian harvestmen that resemble others could be explained by convergent evolution.[26]
Secondary defences
Secondary defences allow for harvestmen to escape and survive from a predator after direct or indirect contact, including
Thanatosis
Some animals respond to attacks by simulating an apparent death to avoid either detection or further attacks.[35] Arachnids such as spiders practise this mechanism when threatened or even to avoid being eaten by female spiders after mating.[36][37] Thanatosis is used as a second line of defence when detected by a potential predator and is commonly observed within the Dyspnoi and Laniatores suborders,[34] with individuals becoming rigid with legs either retracted or stretched.[38][39][40][41]
Freezing
Freezing – or the complete halt of movement – has been documented in the family Sclerosomatidae.[42] While this can mean an increased likelihood of immediate survival, it also leads to reduced food and water intake.[43]
Bobbing
To deflect attacks and enhance escape, long-legged species – commonly known as daddy long-legs – from the Eupnoi suborder, use two mechanisms. One is bobbing, for which these particular individuals bounce their bodies. It potentially serves to confuse and deflect any identification of the exact location of their bodies.[26][43][44][45] This can be a deceiving mechanism to avoid predation when they are in a large aggregation of individuals, which are all trembling at the same time.[26][46] Cellar spiders (Pholcidae) that are commonly mistaken for daddy long-legs (Opiliones) also exhibit this behavior when their webs are disturbed or even during courtship.[47]
Autotomy
Autotomy is the voluntary amputation of an appendage and is employed to escape when restrained by a predator.[48][49][50][51] Eupnoi individuals, more specifically sclerosomatid harvestmen, commonly use this strategy in response to being captured.[46][52][53] This strategy can be costly because harvestmen do not regenerate their legs,[26] and leg loss reduces locomotion, speed, climbing ability, sensory perception, food detection, and territoriality.[46][53][52][54]
Autotomised legs provide a further defence from predators because they can twitch for 60 seconds to an hour after detachment.[50] This can also potentially serve as deflection from an attack and deceive a predator from attacking the animal. It has been shown to be successful against ants and spiders.[39]
The legs continue to twitch after they are detached because 'pacemakers' are 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 harvestman's legs twitch for a minute, others have been recorded to twitch up to an hour. The twitching has been hypothesised to function as an evolutionary advantage by keeping the attention of a predator while the harvestman escapes.[2]
Fleeing
Individuals that are able to detect potential threats can flee rapidly from attack. This is seen with multiple long-legged species in the Leiobunum clade that either drop and run, or drop and remain motionless.[55] This is also seen when disturbing an aggregation of multiple individuals, where they all scatter.[26][46]
Stridulation
Multiple species within the Laniatores and Dyspnoi possess stridulating organs, which are used as intraspecific communication and have also been shown to be used as a second line of defense when restrained by a predator.[34]
Retaliation
Armored harvestmen in Laniatores can often use their modified morphology as weapons.[20][56][57] Many have spines on their pedipalps, back legs, or bodies.[26][58] By pinching with their chelicerae and pedipalps, they can cause harm to a potential predator.[20] Also this has been proven to increase survival against recluse spiders by causing injury, allowing the harvestman to escape from predation.[57]
Chemical
Harvestmen are well known for being chemically protected. They exude strongly odored secretions from their scent glands, called ozopores,[26][28][33][40][59] that act as a shield against predators; this is the most effective defense they use which creates a strong and unpleasant taste.[56] In Cyphophthalmi the scent glands release naphthoquinones, chloro-naphthoquinones and aliphatic methyl ketones, Insidiatores use nitrogen-containing substances, terpenes, aliphatic ketones, and phenolics, while Grassatores use alkylated phenolics and benzoquinones, and Palpatores use substances like naphthoquinones, methyl- and ethyl-ketones, and naphthoquinones.[60] These secretions have successfully protected the harvestmen against wandering spiders (Ctenidae),[20][21] wolf spiders (Lycosidae) and Formica exsectoides ants.[25] However, these chemical irritants are not able to prevent four species of harvestmen being preyed upon by the black scorpion Bothriurus bonariensis (Bothriuridae).[22] These secretions contain multiple volatile compounds that vary among individuals and clades.[61][62][63]
Endangered status
All
Several Opiliones in Argentina appear to be vulnerable, if not endangered. These include Pachyloidellus fulvigranulatus, which is found only on top of
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 United States. 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 restricted habitats of central California are being considered for listing as endangered species, but as yet receive no protection.
Misconception
An
Research
Harvestmen are a scientifically neglected group. Description of new taxa has always been dependent on the activity of a few dedicated taxonomists. Carl Friedrich Roewer described about a third (2,260) of today's known species from the 1910s to the 1950s, and published the landmark systematic work Die Weberknechte der Erde (Harvestmen of the World) in 1923, with descriptions of all species known to that time. Other important taxonomists in this field include:
- Pierre André Latreille (18th century)
- Carl Ludwig Koch, Maximilian Perty (1830s–1850s)
- Tord Tamerlan Teodor Thorell(1860s–1870s)
- Eugène Simon, William Sørensen (1880s–1890s)
- James C. Cokendolpher, Raymond Forster, Clarence and Marie Goodnight, Jürgen Gruber, Reginald Frederick Lawrence, Jochen Martens, Cândido Firmino de Mello-Leitão (20th century)
- Gonzalo Giribet, Adriano Brilhante Kury, Tone Novak (21st century)
Since the 1990s, study of the biology and ecology of harvestmen has intensified, especially in South America.[2]
Early work on the developmental biology of Opiliones from the mid-20th century was resurrected by Prashant P. Sharma, who established Phalangium opilio as a model system for the study of arachnid comparative genomics and evolutionary-developmental biology.
Phylogeny
Harvestmen are ancient
Etymology
The Swedish naturalist and arachnologist Carl Jakob Sundevall (1801–1875) honored the naturalist Martin Lister (1638–1712) by adopting Lister's term Opiliones for this order, known in Lister's days as "harvest spiders" or "shepherd spiders", from Latin opilio, "shepherd"; Lister characterized three species from England (although not formally describing them, being a pre-Linnaean work).[68] In England, the Opiliones are called harvestmen, not because they appear at that season, but from a superstitious belief that if one is killed there will be a bad harvest that year.[69]
Systematics
The interfamilial relationships within Opiliones are not yet fully resolved, although significant strides have been made in recent years to determine these relationships. The following list is a compilation of interfamilial relationships recovered from several recent phylogenetic studies, although the placement and even monophyly of several taxa are still in question.[70][71][72][73][74]
- Suborder Cyphophthalmi Simon, 1879 (about 200 species)
- Infraorder Boreophthalmi Giribet, 2012
- Family Sironidae Simon, 1879
- Family Stylocellidae Hansen & Sørensen, 1904
- Infraorder ScopulophthalmiGiribet, 2012
- Family Pettalidae Shear, 1980
- Infraorder SternophthalmiGiribet, 2012
- Family Troglosironidae Shear, 1993
- Superfamily Ogoveoidea Shear, 1980
- Family Neogoveidae Shear, 1980
- Family Ogoveidae Shear, 1980
- Infraorder (indet).
- Family Parasironidae Karaman, Mitov & Snegovaya, 2024
- Infraorder Boreophthalmi Giribet, 2012
- Suborder Eupnoi Hansen & Sørensen, 1904 (about 1,800 species)
- Superfamily CaddoideaBanks, 1892
- Family Caddidae Banks, 1892
- Superfamily Phalangioidea Latreille, 1802
- Family Globipedidae Kury & Cokendolpher, 2020
- Family Neopilionidae Lawrence, 1931
- Family Phalangiidae Latreille, 1802
- Family Protolophidae Banks, 1893
- Family Sclerosomatidae Simon, 1879
- Superfamily
- Suborder Dyspnoi Hansen & Sørensen, 1904 (about 400 species)
- Superfamily Acropsopilionoidea Roewer, 1923
- Family Acropsopilionidae Roewer, 1923
- Superfamily Ischyropsalidoidea Simon, 1879
- Family Ischyropsalididae Simon, 1879
- Family SabaconidaeDresco, 1970
- Family Taracidae Schönhofer, 2013
- Superfamily Troguloidea Sundevall, 1833
- Family DicranolasmatidaeSimon, 1879
- Family Nemastomatidae Simon, 1872
- Family Nipponopsalididae Martens, 1976
- Family Trogulidae Sundevall, 1833
- Family
- Superfamily Acropsopilionoidea Roewer, 1923
- Suborder Laniatores Thorell, 1876 (about 4,200 species)
- Infraorder Insidiatores Loman, 1900
- Superfamily Travunioidea Absolon & Kratochvil, 1932
- Family Cladonychiidae Hadži, 1935
- Family Cryptomastridae Derkarabetian & Hedin, 2018
- Family Paranonychidae Briggs, 1971
- Family Travuniidae Absolon & Kratochvil, 1932
- Superfamily Triaenonychoidea Sørensen, 1886
- Family Synthetonychiidae Forster, 1954
- Family Triaenonychidae Sørensen, 1886
- Superfamily Travunioidea Absolon & Kratochvil, 1932
- Infraorder Grassatores Kury, 2002
- Superfamily Assamioidea Sørensen, 1884
- Family Assamiidae Sørensen, 1884
- Family Pyramidopidae Sharma and Giribet, 2011
- Family Suthepiidae Martens, 2020
- Family Trionyxellidae Roewer, 1912
- Superfamily Epedanoidea Sørensen, 1886
- Family Epedanidae Sørensen, 1886
- Family Petrobunidae Sharma and Giribet, 2011
- Family Podoctidae Roewer, 1912
- Family Tithaeidae Sharma and Giribet, 2011
- Superfamily Gonyleptoidea Sundevall, 1833
- Family Agoristenidae Šilhavý, 1973
- Family Ampycidae Kury, 2003
- Family Askawachidae Kury & Carvalho, 2020
- Family Cosmetidae Koch, 1839
- Family Cranaidae Roewer, 1913
- Family Cryptogeobiidae Kury, 2014
- Family Gerdesiidae Bragagnolo, 2015
- Family Gonyleptidae Sundevall, 1833
- Family Manaosbiidae Roewer, 1943
- Family Metasarcidae Kury, 1994
- Family Nomoclastidae Roewer, 1943
- Family Otilioleptidae Acosta, 2019
- Family Prostygnidae Roewer, 1913
- Family Stygnidae Simon, 1879
- Family Stygnopsidae Sørensen, 1932
- Superfamily Phalangodoidea Simon, 1879
- Family Phalangodidae Simon, 1879
- Superfamily Samooidea Sørensen, 1886
- Family Biantidae Thorell, 1889
- Family Samoidae Sørensen, 1886
- Family Stygnommatidae Roewer, 1923
- Superfamily SandokanoideaÖzdikmen & Kury, 2007
- Family Sandokanidae Özdikmen & Kury, 2007
- Superfamily Zalmoxoidea Sørensen, 1886
- Family Escadabiidae Kury & Pérez, 2003
- Family FissiphalliidaeMartens, 1988
- Family Guasiniidae Gonzalez-Sponga, 1997
- Family Icaleptidae Kury & Pérez, 2002
- Family Kimulidae Pérez González, Kury & Alonso-Zarazaga, 2007
- Family Zalmoxidae Sørensen, 1886
- Superfamily Assamioidea Sørensen, 1884
- Infraorder Insidiatores Loman, 1900
The family
Fossil record
Despite their long history, few harvestman fossils are known. This is mainly due to their delicate body structure and terrestrial habitat, making them unlikely to be found in sediments. As a consequence, most known fossils have been preserved within amber.
The oldest known harvestman, from the 410-million-year-old Devonian Rhynie chert, displayed almost all the characteristics of modern species, placing the origin of harvestmen in the Silurian, or even earlier. A recent molecular study of Opiliones, however, dated the origin of the order at about 473 million years ago (Mya), during the Ordovician.[75]
No fossils of the
Naturally, most finds are from comparatively recent times. More than 20 fossil species are known from the Cenozoic, three from the Mesozoic,[67] and at least seven from the Paleozoic.[76]
Paleozoic
The 410-million-year-old Eophalangium sheari is known from two specimens, one a female, the other a male. The female bears an
Brigantibunum listoni from East Kirkton near Edinburgh in Scotland is almost 340 million years old. Its placement is rather uncertain, apart from it being a harvestman.
From about 300 Mya, several finds are from the
While the two described Nemastomoides species are currently grouped as Dyspnoi, they look more like Eupnoi.Kustarachne tenuipes was shown in 2004 to be a harvestman, after residing for almost one hundred years in its own arachnid order, the "Kustarachnida".
Some fossils from the Permian are possibly harvestmen, but these are not well preserved.
Described species
- Eophalangium sheari Dunlop, 2004 (Tetrophthalmi) — Early Devonian (Rhynie, Scotland)
- Early Carboniferous (East Kirkton, Scotland)
- Upper Carboniferous (Western Missouri, U.S.)
- )
- Hastocularis argus Garwood, 2014 (Tetrophthalmi) — Upper Carboniferous (Montceau-les-Mines, France)
- Mazon Creek, U.S.)
- Mazon Creek, U.S.)
- Nemastomoididae) — Upper Carboniferous (Commentary, France)
- Nemastomoididae) — Upper Carboniferous (Mazon Creek, U.S.)
Mesozoic
Currently, no fossil harvestmen are known from the
A fossil of Halitherses grimaldii, a long-legged Dyspnoi with large eyes, was found in Burmese amber dating from approximately 100 Mya. It has been suggested that this may be related to the Ortholasmatinae (Nemastomatidae).[78]
Cenozoic
Unless otherwise noted, all species are from the Eocene.
- Geiseltal, Germany
- Philacarus hispaniolensis (Laniatores: Samoidae?) — Dominican amber
- Kimula species (Laniatores: Kimulidae) — Dominican amber
- Hummelinckiolus silhavyi Cokendolpher & Poinar, 1998 (Laniatores: Samoidae) — Dominican amber
- Caddo dentipalpis (Eupnoi: Caddidae) — Baltic amber
- Dicranopalpus ramiger (Koch & Berendt, 1854) (Eupnoi: Phalangiidae) — Baltic amber
- Opilio ovalis (Eupnoi: Phalangiidae?) — Baltic amber
- Cheiromachus coriaceus Menge, 1854 (Eupnoi: Phalangiidae?) — Baltic amber
- Leiobunum longipes (Eupnoi: Sclerosomatidae) — Baltic amber
- Histricostoma tuberculatum (Dyspnoi: Nemastomatidae) — Baltic amber
- Mitostoma denticulatum (Dyspnoi: Nemastomatidae) — Baltic amber
- Nemastoma incertum (Dyspnoi: Nemastomatidae) — Baltic amber
- Sabaconidae) — Baltic amber
- Florissant Fossil Beds National Monument, USA (Oligocene)
- Proholoscotolemon nemastomoides (Laniatores: Cladonychiidae) — Baltic amber
- Siro platypedibus (Cyphophthalmi: Sironidae) — Bitterfeld amber
- Amauropilio atavus (Cockerell, 1907) (Eupnoi: Sclerosomatidae) — Florissant, USA (Oligocene)
- Amauropilio lacoei (A. lawei?) (Petrunkevitch, 1922) — Florissant, USA (Oligocene)
- Pellobunus proavus Cokendolpher, 1987 (Laniatores: Samoidae) — Dominican amber
- Phalangium species (Eupnoi: Phalangiidae) — near Rome, Italy (Quaternary)
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- ^ a b Dias, B.C., Willemart, R.H., 2013. The effectiveness of post-contact defenses in a prey with no pre-contact detection. Zoology 116, 168–174.
- ^ a b Segovia, J.M.G., Del-Claro, K., Willemart, R.H., 2015. Defences of a Neotropical harvestman against different levels of threat by the recluse spider. Behaviour 152, 757–773.
- ^ Eisner, T., Eisner, M., Siegler, M., 2005. Secret Weapons: Defenses of Insects, Spiders, Scorpions, and Other Many-legged Creatures. Harvard University Press.
- ^ Shultz, J.W., Pinto-da-Rocha, R., 2007. Morphology and functional anatomy. Harvest. Biol. Opiliones Harv. Univ. Press Camb. Mass. Lond. Engl. 14–61.
- ^ A Novel Class of Defensive Compounds in Harvestmen: Hydroxy-γ-Lactones from the Phalangiid Egaenus convexus
- ^ Gnaspini, P., Rodrigues, G.S., 2011. Comparative study of the morphology of the gland opening area among Grassatores harvestmen (Arachnida, Opiliones, Laniatores)of Zoological Systematics and Evolutionary Research.
- ^ Hara, M.R., Gnaspini, P., 2003. Comparative study of the defensive behavior and morphology of the gland opening area among harvestmen (Arachnida, Opiliones, Gonyleptidae) under a phylogenetic perspective.
- ^ Shear, W.A., Jones, T.H., Guidry, H.M., Derkarabetian, S., Richart, C.H., Minor, M., Lewis, J.J., 2014. Chemical defenses in the opilionid infraorder Insidiatores: divergence in chemical defenses between Triaenonychidae and Travunioidea and within travunioid harvestmen (Opiliones) from eastern and western North America | Journal of Arachnology.
- ISBN 978-0-674-05356-4.
- ^ The Spider Myths Site: "Daddy-Longlegs" Archived 2007-07-14 at the Wayback Machine
- ^ Perkins, Sid (June 23, 2009). "Long-lasting daddy longlegs". Science News.
- ^ S2CID 9570512. Archived from the original(PDF) on 2016-03-05. Retrieved 2012-12-21.
- ^ Martin Lister's English Spiders, 1678. Ed. John Parker and Basil Hartley (1992). Colchester, Essex: Harley Books. pp. 26 & 30. (Translation of the Latin original, Tractatus de Araneis.)
- ^ Frank Cowan, Curious Facts in the History of Insects, p.321
- ISSN 1095-8312.
- S2CID 84029705.
- ^ Fernández R, Sharma PP, Tourinho AL, Giribet G. 2017 The Opiliones tree of life: shedding light on harvestmen relationships through transcriptomics. Proc. R. Soc. B 284: 20162340. https://dx.doi.org/10.1098/rspb.2016.2340
- S2CID 85408627.
- PMID 25425936.
- PMID 25120562.
- ISBN 978-0-674-02343-7.
- Christian Science Monitor. Retrieved April 16, 2014.
- PMID 16024358.
External links
- Joel Hallan's Biology Catalog[permanent dead link] (2005)
- 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—A synoptic taxonomic arrangement of the order Opiliones, down to family-group level, including some photos of the families
- Pocock, Reginald Innes (1911). . Encyclopædia Britannica (11th ed.).