- only species with images listed
Images and Species Descriptions
Text and photographs © 2011 Jørgen Lissner
The Spiders of Europe and Greenland
Family: Theridiosomatidae (Ray Spiders)
Biology: This is a small family of which almost all species are distributed in the tropics, with most species found in South America. Several theridiosomatid genera build orb webs distorted into a conical shape. Theridiosoma gemmosum is the only European representative of the family.
Characters of family: Eyes heterogeneous. Both eyerows are procurved, the posterior row much more so than the anterior. The palps of female members of the family lack the claw, which set them apart from members of the families Araneidae and Theridiidae. The chelicers also lack a boss (condyles) laterally at their bases. This feature also separates the family from the Araneida in which the boss is prominent. The chelicers does not possess areas with parallel striae (stridulation organ) typical of most Linyphiid spiders. A relatively large appendage (colulus) is present in front of the anterior spinnerets. The colulus is probably derived from ancestral spinners and is functionless. A colulus is only present in a minority of families (e.g. the Theridiidae and Thomisidae) and its relative size is important, and used for identification to family and sometimes genus level. The members of the Theridiosomatidae do not have comb bristles on the dorsal side of tarsus IV that separates them from the Theridiidae in which some members have similar general appearance.
Taxonomic note: The Theridiosoma genus was once included in the orb weaver family (Araneidae) due to the general appearance of the species, and since they weave a modified orb web. However, they are distinguished from the Araneidae by the relatively large space between the anterior row of eyes and the anterior edge of the carapace (referred to as the widht or height of clypeus). Theridiosomatidae spiders have the height of clypeus higher than the distance between the anterior and posterior median eyes.
This family is represented in Europe with 1 species in one genus (van Helsdingen, 2009; Platnick, 2009). European genus (number of species in parenthesis): Theridiosoma (1).
Genus: Theridiosoma O. P.-Cambridge, 1879
Characters of genus: Largest genus of the family but only one species is known from europe. Most species are less than 3 mm The globular abdomen greatly overhangs the posterior parts of the carapace. The species resemble small members of the Theridiidae. The median ocular trapezium is longer than broad. The posterior medial eyes are larger than the posterior laterals. The distance between the posterior medial eyes are shorter than the distance between a median and a lateral eye. The sternum is broadly truncated at rear. Labium is much broader than wide. Femur I is several times thicker than femur IV.
There is 1 European species (van Helsdingen, 2009; Platnick, 2009): Theridiosoma gemmosum.
Theridiosoma gemmosum (L. Koch, 1877)
Description: The anterior medial eyes are surrounded by black pigmentation. Carapace is yellow brown to dark brown with variable darker markings. Sternum is dark brown with yellow midline. Femora and tibia I thickened, femora and tibia II less so. The leg colour varies from yellow to dark brown, usually femora are dark brown apically, and the patella uniformly dark brown while remaining segments are lighter. The legs are spineless, except for one spine on femur I. Abdomen globose, higher than long, dorsal surface with silvery spots isolated by dark brown reticulations. Some silvery spots may have an orange tint. Midline area lacks spots in some places, however the exact pattern is very variable among individual spiders. Usually there are som transverse bars or wedges. Each side of the abdomen usually has dark areas lacking silvery spots. Males are less globose than females and the dark areas of the abdomen are sometimes larger than in the female and the light spots are less silvery. Palps of adult males are quite large compared to the body size. The species constructs small, modified orb webs, of which 2-5 radii converge before gathering at the centre of the web. A single thread is attached to nearby vegetation, and is held by the spider staying in the centre of the web. The thread is drawn tight such as the web is pulled into a conical shape. When prey encounters the web, the thread is slackened to enhance entangling. The females construct small spherical egg sacs with a brownish papery surface. The sacks are attached to the vegetation by long whitish stalks, usually higher up than the web. The egg sacks are very characteristic, and reveal the presence of Theridiosoma even if no specimens are found. Spiders of the Mimetidae construct egg sacks not unlike those of Theridiosoma, however they differ by having a woolly surface. Size: Female 2-3 mm; male 1.5-2 mm. Maturity: Males from May until June, females also until September. Habitat: Wet,more or less permanently flooded places with dense vegetation in wetlands, including lakeshores. The webs are built close to the water surface, usually under dark condtions such as under overhanging vegetation. Range: Austria, Belgium, Bulgaria, Croatia, Czech Republic, Denmark, France (Corsica), France (Mainland), Germany, Great Britain (Mainland), Greece (Mainland), Hungary, Ireland, Italy (Mainland), Netherlands, Poland, Russia (Central European), Russia (Eastern European), Russia (Southern European), Slovakia, Slovenia, Spain (Mainland), Sweden, Switzerland, Ukraine (van Helsdingen 2009.1). Global range: North America, Europe to Central Asia (Platnick 10.0).
Male abdominal markings.