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Porrhomma convexum  (Westring, 1851)
≤ 1900   1901-1979   1980-2005   2006 ≤
Description: A fairly large Porrhomma species. Carapace yellow-brown to blackish brown. Ocular area with forward projecting hairs. Abdomen greyish black. Legs yellow-brown. Femur I with one or two dorsal spines and without prolateral spine. All metatarsi spineless. Tm I 0.4-0.49 (Roberts 1987). Size: Female 2.2-3.0 mm; male 2.2-3.0 mm.

Genus: Porrhomma Simon, 1884. Characters of genus: There is no recent revision of the genus available. The description here is based on Locket & Millidge (1953), and Borges & Wunderlich (2008). Ocular area with some forward projecting hairs, most pronounced in males. Eyes are variable in size, in some species minute or absent. Metatarsus IV without a trichobothrium. The species differ in leg spination, a character that is useful for grouping the species aiding identification. Male palp with no tibial apophysis. Some species possess stridulating files on coxa I while these are reduced or absent in others. The latter case is considered a derived (apomorphic) character of the genus. Tm I of British species range between 0.3-0.64 (Roberts 1987).

Family: Linyphiidae Blackwall, 1859 (Line Weaving Spiders). Characters of family: The linyphiids belong to the group of ecribellate spider families having 8 eyes and 3 tarsal claws. The eyes are arranged in 2 rows of 4, usually heterogeneous in size with the anterior medials smaller than the rest. Frequently, the eyes are ringed with black, this being most noticeable in species with lighter coloured carapaces such as many species of the Linyphiinae subfamily. Some species adapted to dark habitats have the eyes much reduced, sometimes being very minute in size or only evidenced by pale markings under the integument (e.g. Porrhomma rosenhauri). The carapace is highly variable especially in the smaller species belonging to the Erigoninae subfamily. Males of this large subfamily frequently have the frontal region modified into strangely formed lobes or bear other types of protuberances some of which may have tufts of hairs. Some species have the carapace punctured with pits (see images of Lophomma punctatum). The males may also have sulci (grooves) running backwards from the posterior eyes. The chelicerae do not possess a lateral condyle (boss at base of chelicer). The outer side of the chelicerae have horizontal stridulating ridges visible in many species. Such ridges only occur scattered in other spider families (see for example images of ridges in Metellina stridulans of the Tetragnathidae). The labium is strongly rebordered as in the Nesticidae, Araneidae, and Tetragnathidae. The endites are usually parallel. Legs are slender and provided with spines. The number of spines on the legs is an important character for species identification when this is undertaken using the stereomicroscope. The abdomen is nearly always longer than wide sometimes with a pattern (Linyphiinae in particular) and sometimes mainly uniformly coloured, very often blackish (Erigoninae in particular). Some species posses an abdominal scutum as for example some members of the Ceratinella genus. The epigynes are variable, sometimes simple as in the Erigoninae or provided with a scapus as often seen in the Linyphiinae. The male palp often possesses an U-shaped paracymbium. The family was earlier divided in to two subfamilies, which sometimes were elevated to family status: the Linyphiidae and Erigonidae (also known as Micryphantidae). The Linyphiidae was characterized by not having tibial apophyses on the male palp, by having a claw on the female palp in most species, and by having two dorsal spines on tibia IV or if only one spine present there was one short spine on metatarsi I and II. The Erigonidae was characterized by having at least one tibial apophyses on the male palp, by lacking a claw on the female palp, and by having just a single dorsal spine on tibia IV and with the metatarsi spineless, or all spines lacking altogether. However, the family is now divided in to seven subfamilies, the Dubiaraneinae, Erigoninae, Ipainae, Linyphiinae, Micronetinae, Mynogleninae, and Stemonyphantinae. Consult recent literature or Wikipedia for lists of subfamily genera. See also Linyphiid Spiders Of The World by Andrei Tanasevitch and LinyGen: Linyphioid Genera of the World (Pimoidae and Linyphiidae) by Gustavo Hormiga, Dimitar Dimitrov, Jeremy A. Miller and Fernando Alvarez-Padilla.
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