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Sexual dimorphism

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Metagyndes chilensis - reared - by Phalagorn (4)

Metagyndes chilensis Roewer, 1943, male and female, showing sharp difference between sexes in gonyleptids. Photo copyright © Phalagorn, from BugNation [1]

Sexual dimorphism in Opiliones is extremely varied and may be apparent in almost all body parts, playing complex and poorly understood roles.

ColorEdit

Leiobunum rupestre (Herbst, 1799) by Silhavy 1956a

Sclerosomatidae, Leiobunum rupestre (Herbst, 1799), both sexes, showing dimorphism in the saddle.

The saddle in Phalangioidea is often much sharper in females, while in males it is more indistinct.

In many Eupnoi and Laniatores, color dimorphism may be so intense that often different sexes ended up described as different species. A striking example is the Brazilian Mitobatinae Metamitobates squalidus (Perty, 1833), in which the female is green with red tints, while the male is mostly yellow.

CarapaceEdit

In some species of Gonyleptoidea the male has greatly developed ocularium, which causes the carapace to grow backwards deforming area I, while in females the ocularium is considerably smaller and the area I is not squeezed.

Dorsal scutumEdit

CheliceraeEdit

The most obvious feature here are the kidney-shaped swollen chelicerae in males of many families such as Agoristenidae, Stygnidae, Cranaidae.

But there are other kinds of dimorphism in the chelicerae, for example spines and protuberances on bulla or most commonly on the cheliceral hand.

Both fingers in some Grassatores (e.g., Podoctidae and Epedanidae) show extreme dimorphism, in the male being extremely robust, twisted or with robust and differentiated dentition.

PedipalpsEdit

Pedipalps may be much elongate (either subtly or immensely) in males only (Cranaidae), or immensely stout, keeled in males (Cranaidae).

There is also dimorphism in length in the families Epedanidae and Stygnidae.

In Podoctidae, while female pedipalps are ordinary cylindrical, those of males may assume bizarre forms, such as a bottle shape.

Villarreal et al - Ventrifurca - Fig 05

Cranaidae, Ventrifurca sp., both sexes, showing subtle dimorphism in the pedipalps. From Villarreal et al. (2015)

Leg IEdit

In some species of Phalangiinae (e.g., in genera Cristina, Phalangium), males may have immensely stout front legs. This is much rarer in Laniatores, where an undescribed Paratricommatus from Brazil shows this feature.

Phalangium kitabense Chemeris, 2012 from Uzbekistan - original description

Phalangium kitabenseChemeris, 2012 male from Uzbekistan, original description.


Tarsus of leg IEdit

MNRJ 18969 Saramacia annulata TAQUA ma do AUTOMTG

Manaosbiidae, Saramacia annulata (Mello-Leitão, 1931), male MNRJ 18969 from Tocantins. Photo copyright (c) AB Kury.

In most Gonyleptoidea, males have thickened glandular basitarsomeres in leg I. More notably so in the males of Manaosbiidae, in which basitarsomeres are fused into a very large spindle. This also occurs in some species of Cosmetidae.

Coxa of leg IVEdit

A well-developed apophysis is a trademark of the Gonyleptidae males, often forming a pincer with a matching apophysis of trochanter IV.


Trochanter of leg IVEdit

Femur of leg IVEdit

Tibia of leg IVEdit

Tibia IV may be strongly incrassate in males of Zalmoxidae (many genera, Zalmoxis), Cryptogeobiidae (some genera such as Cryptogeobius).



Tarsi of legs III-IVEdit

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