Homalonychus
| Homalonychus | ||||||||||||
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Homalonychus sp. |
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Homalonychidae | ||||||||||||
| Simon , 1893 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Homalonychus | ||||||||||||
| Marx , 1891 |
Homalonychus is the only genus of the Homalonychidae family within the real spiders and includes only three species .
description
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The adult males reach a body length of six to nine millimeters and the females from seven to 13 millimeters. The body and legs are usually covered with fine soil particles , except in adult males . The skin is orange-brown, while the chelicerae , mouthparts, "forehead" (clypeus) and sides of the head are darker in color.
Members of the genus Homalonychus have eight eyes which, like usually only the secondary eyes of the real spider, resemble the basic structure of the eyes of vertebrates , i.e. are equipped with a boat-shaped tapetum .
The back shield (carapace) is spotted; the darker spots are usually arranged on the hips (coxa). The front spots run with the darker sides. The thighs (femur) of the treads with four spots on the top (dorsal), the basal of which is triangular and the distal may be absent. The carapace has a clearly demarcated head / eye region and a clear and deep thoracic furrow . The front part of the body is rounded towards the sides and is widest and arched in the area of the thoracic furrow (second and third pair of legs).
In females and not yet sexually mature males, the carapace is densely covered with short, toothed or hairy bristles (setae) that become thicker in the dark areas. Adult males and all females have longer, microscopically fine hairs and bristles on the carapace and abdomen (opisthosoma, abdomen). The soil particles from the surroundings adhere to these flattened and soft or blade-like hairs and bristles.
In the female the legs are approximately the same length, the third pair of legs is the shortest; for the males the leg formula is I = IV, II, III. The legs are thorny, have bristles, hair and trichobothria ; chemosensitive hair is also present.
The Homalonychus TYPES have six spinnerets on the Collulus missing. The epigyne is relatively large, while the internal genital organs of the female are relatively simple; just like the bulbs of the male. The most important and safest determinant is the epigyne.
Reproduction and development
According to Roth (1984), nothing is known about the reproductive behavior. Vetter and Cokendorfer found in 1999 that the females of Homalonychus theologus each produce a sand-covered, hollow Eisack approx. 18 mm in diameter, the inside of which is lined with spider silk. The Eisack is hung on the underside of their hiding places (under stones or solid floor slabs), whereby the sand cover serves as camouflage, the placement under stones minimizes the sun exposure and danger and the cavity construction presumably keeps the humidity and temperature stable for the eggs hung inside. Inside, depending on the nutritional situation, 20 to 25 (or more) eggs are hung. After about 50 days, about 20 spiderlings hatch , whereby the entire development time, including development of the eggs before oviposition, should be longer. The young shed their skin at least once in their hiding place.
Adult animals live at least two years. In more than 270 faunistic recordings, immature individuals were common finds throughout the year, with more being found in spring than in the second half of the year; However, this result allows conclusions to be drawn about the behavior of the arachnologists rather than that of the spiders. The females were most frequently found between December and June, while males were only found in four recordings in April. A collection in October showed both males and females together.
Way of life
Members of the family are, as far as is known, nocturnal hunters wandering around without a net , who can be found in deserts and semi-deserts in fine sand or soil under loose rubble, under stones or in detritus . The shed skin can often be found clinging to the underside of flat stones. So far, no caves or the like have been found in which the animals retreat during the day. Apparently they have no prey preference, but moths and flies have proved themselves to be acceptable in keeping them .
camouflage
Females and male juveniles camouflage themselves with the finest soil particles from 48 µm to 120 µm in diameter, which stick to the setae. Thus, they take on both the color and structure of the soil in their living space. Similar behavior can also be applied Cryptothele ( Zodariidae ), Sicarius ( Sicariidae ) Paratropis ( Paratropididae ) Microstigmata ( Microstigmatidae ) and Bradystichus ( Bradystichidae ), as well as the Weber servants of the genus Trogulus ( Trogulidae be observed). Homalonychus , similar to the Sicarius in Chile, rest with their legs outstretched and are often lightly buried in the ground.
The primary protective mechanisms of the species are their nocturnal activity and the camouflage with soil particles supported by their hairiness. In the resting position, the spider positions itself with all legs stretched out from each other. If she is disturbed, Homalonychus theologus pushes her legs into a rigid, 2-pair formation by stretching the two front pairs of legs forward and the two rear pairs of legs backwards. This posture is triggered when the animal is touched or otherwise disturbed, and is therefore interpreted as a defensive position, which is very often assumed by other spiders when they are in danger from predators. Juvenile animals do not exhibit this behavior. The rigidity is maintained until one takes the animal in hand. Only then does an escape reaction begin . The observations are based on a few catches; the behavior of Homalonychus theologus has not yet been sufficiently investigated. What remains a mystery is the difference to other weaving spiders, who bend their legs instead of stretching them out during the dead reflex . Since it is also doubted that the possible predators of Homalonychus theologus can count and have a food preference for eight instead of four-legged prey, this atypical behavior gives rise to speculation. It is possible that Homalonychus theologus is imitating the remains of a dried-up cactus with its thorns.
Systematics
The species are occasionally still counted among the Zodariidae , e.g. B. by Jörg Wunderlich (2004). The considerations to assign the Homalonychus to another family were based on similarities in morphological characteristics, which, according to Roth and in the opinion of most arachnologists, have not yet proven to be sufficiently decisive for a family assignment. The genus Megapyge was therefore transferred to the Thomisidae , and Homalonychus joyaus to the genus Storenomorpha (Zodariidae). The combination of two features, namely the absence of saw teeth on the chewing tools ( serrula on the Gnathocoxes ), as well as the absence of teeth on the paired tarsal claws , would distinguish the Homalonychidae from all other relevant families. It is therefore "preferable to group the Homalonychidae in a separate family". The assignment to other families is probably based on previous and further incorrect assignments of some Indian species to the genus Homalonychus . The assignment to a superfamily remains unclear. A supergrouping "Homalonychiformia" for Homalonychidae and Cithaeronidae as well as the assignment to the superfamily Pisauroidea was discussed .
The World Spider Catalog currently lists only three species for the genus Homalonychus . (As of June 2016)
- Homalonychus raghavai Patel & Reddy , 1991 - The species is endemic to India . In addition to their endemic nature in an extreme habitat, their camouflage abilities and the way their ice bags are made are remarkable.
- Homalonychus selenopoides Marx , 1891 ( Syn .: Homalonychus positivus Chamberlin , 1924 ) - The species occurs exclusively in northwestern Mexico , Arizona and southern California and is absent on Baja California
- Homalonychus theologus Chamberlin , 1924 - The species occurs exclusively in the deserts and semi-deserts of Southern California and Baja California up to about 600 meters above sea level.
Web links
Homalonychidae in the World Spider Catalog Homalonychus in the World Spider Catalog
literature
- Vincent D. Roth (1984): The Spider Family Homalonychidae (Arachnida, Araneae). The American Museum of Natural History, American Museum Novitates, 2790, pp. 1–11, New York 1984. ( PDF ; 2.84 MB)
Individual evidence
- ↑ a b c Natural History Museum of the Burgergemeinde Bern: World Spider Catalog Version 17.0 - Homalonychus . Retrieved June 2, 2016.
- ↑ Foelix, Rainer F. 1979. Biology of the spiders. Georg Thieme Verlag Stuttgart. ISBN 3-13-575801-X
- ^ A b Richard S. Vetter, James C. Cokendolpher: Homalonychus theologus (Araneae, Homalonychidae): Description of Eggsacs and a Possible Defensive Posture. The Journal of Arachnology, 28, pp. 361–363, 2000 (PDF; 255 kB)
- ↑ Wunderlich, J. (2004): The fossil spiders (Araneae) of the family Zodariidae in Baltic amber, with remarks on their subfamilies including the Cryptothelinae and the Homalonychinae. Contribution Araneol. 3: 1578-1611. Quoted in Platnick, 2007.