Harvestman phylogeny
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| Opiliones Fossil range: Devonian - Recent |
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Harvestmen are an order of arachnids. Although they are often confused with spiders, the two orders are not closely related. Research on harvestman phylogeny is in a state of flux. While some families are clearly monophyletic, that is share a common ancestor, others are not, and the relationships between families are often not well understood.
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[edit] Position in Arachnida
The relationship of harvestmen with other arachnid orders is still not sufficiently resolved.
Up until the 1980s they were thought to be closely related to mites (Acari). Shultz (1990) proposed to group them with scorpions, pseudoscorpions and Solifugae ("camel spiders"); he named this clade Dromopoda. This view is currently widely accepted. However, the relationships of the orders within Dromopoda are not yet sufficiently resolved. When only considering recent taxa (Shultz 1990), the harvestmen appear as a sister group to Novogenuata (Scorpions, Pseudoscorpions, Solifugae).
Dromopoda |
Dromopoda |
When also considering fossils (Giribet et al. 2002), the harvestmen are sister to Haplocnemata (Pseudoscorpions and Solifugae).[1]
[edit] Relationship of suborders
Latreille (1796) erected the family Phalangida [sic] for the then known harvestmen, but included the genus Galeodes (Solifugae). Thorell (1892) recognized the suborders Palpatores, Laniatores, Cyphophthalmi (called Anepignathi), but also included the Ricinulei as a harvestman suborder. The latter were removed from the Opiliones by Hansen and Sørensen (1904), rendering the harvestmen monophyletic.
(after Giribet et al. 2002) |
(after Shultz 1998) |
According to current research, the Cyphophthalmi, the most basal suborder, are a sister group to all other harvestmen, which are according to this system called Phalangida. The Phalangida consist of three suborders, the Eupnoi, Dyspnoi and Laniatores. While these three are each monophyletic, it is not clear how exactly they are related. Giribet et al. 2002 come to the conclusion that Dyspnoi and Laniatores are sister groups, and call them Dyspnolaniatores, which are sister to Eupnoi. This is in contrast to the classical hypothesis that Dyspnoi and Eupnoi form a clade called Palpatores. As other recent studies support the latter, this topic is currently debated.[1]
[edit] Relationship within suborders
[edit] Cyphophthalmi
The Cyphophthalmi have been divided into two infraorders, Temperophthalmi (including the superfamily Sironoidea, with the families Sironidae, Troglosironidae and Pettalidae) and Tropicophthalmi (with the superfamilies Stylocelloidea and its single family Stylocellidae, and Ogoveoidea, including Ogoveidae and Neogoveidae); however, recent studies suggest that the Sironidae, Neogoveidae and Ogoveidae are not monophyletic, while the Pettalidae and Stylocellidae are. The division into Temperophthalmi and Tropicophthalmi is not supported, with Troglosironidae and Neogoveidae probably forming a monophyletic group. The Pettalidae are possibly the sister group to all other Cyphophthalmi.
While most Cyphophthalmi are blind, eyes do occur in several groups. Many Stylocellidae, and some Pettalidae bear eyes near or on the ozophores, as opposed to most harvestmen, which have eyes located on top. The eyes of Stylocellidae could have evolved from the lateral eyes of other arachnids, which have been lost in all other harvestmen. Regardless of their origin, it is thought that eyes were lost several times in Cyphophthalmi.
Spermatophores, which normally do not occur in harvestmen, but in several other arachnids, are present in some Sironidae and Stylocellidae.[1]
[edit] Eupnoi
The Eupnoi are currently divided into two superfamilies, the Caddoidea and Phalangioidea. The Phalangioidea are assumed to be monophyletic, although only the families Phalangiidae and Sclerosomatidae have been studied; the Caddoidea have not been studied at all in this regard. The limits of families and subfamilies in Eupnoi are uncertain in many cases, and are in urgent need of further study.[1]
[edit] Dyspnoi
(after Giribet & Kury 2007) |
.jpg/250px-Sabacon_cavicolens_(Marshal_Hedin).jpg)
The Dyspnoi are probably the best studied harvestman group regarding phylogeny. They are clearly monophyletic, and divided into two superfamilies. The relationship of the superfamily Ischyropsalidoidea, comprised of the families Ceratolasmatidae, Ischyropsalididae and Sabaconidae, has been investigated in detail. It is not clear wether Ceratolasmatidae and Sabaconidae are each monophyletic, as the ceratolasmatid Hesperonemastoma groups with the sabaconid Taracus in molecular analyses. All other families are grouped under Troguloidea.[1]
[edit] Laniatores
.jpg/250px-Fumontana_deprehendor_(Marshal_Hedin).jpg)
There is not yet a proposed phylogeny for the whole group of Laniatores, although some families have been researched in this regard. The Laniatores are currently divided into two infraorders, the "Insidiatores" Loman, 1900 and the Grassatores Kury, 2002. However, Insidiatores is probably paraphyletic. It consists of the two superfamilies Travunioidea and Triaenonychoidea, with the latter closer to the Grassatores. Alternatively, the Pentanychidae, which currently reside in Travunioidea, could be the sister group to all other Laniatores.
The Grassatores are traditionally divided into the Samooidea, Assamioidea, Gonyleptoidea, Phalangodoidea and Zalmoxoidea. Several of these groups are not monophyletic. Molecular analyses relying on nuclear ribosomal genes support monophyly of Gonyleptidae, Cosmetidae (both Gonyleptoidea), Stygnopsidae (currently Assamioidea) and Phalangodidae. The Phalangodidae and Oncopodidae may not form a monophyletic group, thus rendering the Phalangodoidea obsolete. The families of the obsolete Assamioidea have been moved to other groups: Assamiidae and Stygnopsidae are now Gonyleptoidea, Epedanidae reside within their own superfamily Epedanoidea, and the "Pyramidopidae" are possibly related to Phalangodidae.[1]
[edit] Fossil record
Despite their long history, few harvestman fossils are known. This is mainly due to their delicate body structure and terrestrial habitat, making it unlikely to be found in sediments. As a consequence, most known fossils have been preserved as amber.
The oldest known harvestman, from the 400 million years old Devonian Rhynie chert, already has almost all the characteristics of modern species, placing the origin of harvestmen in the Silurian, or even earlier.
Interestingly, no fossils of Cyphophthalmi or Laniatores much older than 50 million years are known, despite the former presenting a basal clade, and the latter having probably diverged from the Dyspnoi more than 300 million years ago.
Naturally, most finds are from comparatively recent times, but it is interesting that while there are more than 20 known species from the Cenozoic, and at least seven from the Paleozoic, only one species from the Mesozoic has yet been found.[2]
[edit] Paleozoic
The 400 million years old Eophalangium sheari is known from two specimens, one a female, the other a male. The female bears an ovipositor and is about 10 mm long, the male penis can be discerned too. It is not definitely known if both sexes belong to the same species. They have long legs, tracheae, and no median eyes.
Brigantibunum listoni from near Edinburgh in Scotland is almost 340 million years old. Its placement is rather uncertain, apart from it being a harvestman.
From about 300 million years ago (mya) there are several finds from the Coal Measures of North America and Europe. 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 hundred years in its own arachnid order, the "Kustarachnida".
There are some fossils from the Permian that are possibly harvestmen, but these are not well preserved.
[edit] Described species
- Eophalangium sheari (Eupnoi) — Early Devonian (Rhynie, Scotland)
- Brigantibunum listoni (Eupnoi?)— Early Carboniferous (East Kirkton, Scotland)
- Eotrogulus fayoli Thevenin, 1901 (Dyspnoi: † Eotrogulidae) — Upper Carboniferous (Commentry, France)
- Nemastomoides elaveris Thevenin, 1901 (Dyspnoi: † Nemastomoididae) — Upper Carboniferous (Commentary, France)
- Nemastomoides longipes Petrunkevitch — Upper Carboniferous (Mazon Creek, USA)
- Kustarachne tenuipes Scudder, 1890 (Eupnoi?) — Upper Carboniferous (Mazon Creek, USA)
- Echinopustulus samuelnelsoni Dunlop, 2004 (Dyspnoi?) — Upper Carboniferous (Western Missouri, USA)
[edit] Mesozoic
No fossil harvestmen are known from the Triassic. They are also so far absent from the Lower Cretaceous Crato Formation of Brazil, which has yielded many other terrestrial arachnids. An unnamed long-legged harvestman was reported from the Early Cretaceous of Koonwarra, Victoria, Australia, which may be a Eupnoi.
Halitherses grimaldii Giribet & Dunlop, 2005 from Burmese amber (c. 100 mya) is a long-legged Dyspnoi with large eyes, which may be related to the Ortholasmatinae (Nemastomatidae).[3]
[edit] Cenozoic
Unless otherwise noted, all species are from the Eocene.
- Trogulus longipes Haupt, 1956 (Dyspnoi: Trogulidae) — 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
- Sabacon claviger (Dyspnoi: Sabaconidae) — Baltic amber
- Petrunkevitchiana oculata (Petrunkevitch, 1922) (Eupnoi: Phalangioidea) — Florissant, 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)
[edit] Footnotes
[edit] References
- Joel Hallan's Biology Catalog (2005)
- Shultz, J.W. (1990): Evolutionary morphology and phylogeny of Arachnida. Cladistics 6: 1-38.
- Shultz, Jeffrey W. (1998): Phylogeny of Opiliones (Arachnida): An Assessment of the "Cyphopalpatores" Concept. Journal of Arachnology 26(3): 257-272. PDF
- Giribet, G., Edgecombe, G.D., Wheeler, W.C. & Babbitt, C. (2002): Phylogeny and systematic position of Opiliones: a combined analysis of chelicerate relationships using morphological and molecular data. Cladistics 18: 5-70.
- Giribet, Gonzalo & Dunlop, Jason A. (2005): First identifiable Mesozoic harvestman (Opiliones: Dyspnoi) from Cretaceous Burmese amber. Proc Biol Sci. 272(1567): 1007-1013. full HTML
- Pinto-da-Rocha, R., Machado, G. & Giribet, G. (eds.) (2007): Harvestmen - The Biology of Opiliones. Harvard University Press ISBN 0-674-02343-9
