''Theridiosoma gemmosum'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Theridiosomatidae, known as

ray spider The ray spiders (Theridiosomatidae) are a family of spiders first described by Eugène Simon in 1881. They are most recognizable for their construction of cone-shaped webs. The family contains several genera which actively hunt for prey by using ...

s. It is widely distributed in the

Holarctic The Holarctic realm is a biogeographic realm that comprises the majority of habitats found throughout the continents in the Northern Hemisphere. It corresponds to the floristic Boreal Kingdom. It includes both the Nearctic zoogeographical reg ...

region. A small spider with a shiny globular

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

, it constructs a conical orb web.

Description

''Theridiosoma gemmosum'' is a small spider. Females are 2–3 mm long, males smaller still at 1.5–2 mm. In both sexes, the carapace (upper surface of the

cephalothorax The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''cepha ...

) is dark brown; the upper surface of the abdomen (

opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to a ...

) is silvery with variable dark lines and marks. The abdomen is globular, more or less circular from above. The male

palpal bulb The two palpal bulbs – also known as palpal organs and genital bulbs – are the copulatory organs of a male spider. They are borne on the last segment of the pedipalps (the front "limbs" of a spider), giving the spider an appearance often descr ...

s and the female

epigyne The epigyne or epigynum is the external genital structure of female spiders. As the epigyne varies greatly in form in different species, even in closely related ones, it often provides the most distinctive characteristic for recognizing species. ...

are distinctive.

Web

''Theridiosoma gemmosum'' constructs a small orb web. The radii do not run directly to a central hub as with other orb webs, but are first joined into groups of two or three before combining to meet in the middle. A single thread runs from the centre to a nearby support, and is held by the spider. While the spider is holding this thread the tension pulls the web into a conical shape, described as "like an umbrella turned inside out". When a prey item hits the web, the spider releases the tension, causing the prey to become more enmeshed.

Taxonomy

The species was first described by Ludwig Koch in 1877, as ''Theridium gemmosum''. (''Theridium'' is an alternative spelling of ''Theridion''.) Koch did not explain the origin of the species name ''gemmosum''. The

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

word ' means "set with jewels"; Koch several times used the description "'",

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

for "

mother of pearl Nacre ( , ), also known as mother of pearl, is an organicinorganic composite material produced by some molluscs as an inner shell layer; it is also the material of which pearls are composed. It is strong, resilient, and iridescent. Nacre is ...

". In 1879,

Octavius Pickard-Cambridge Octavius Pickard-Cambridge Fellow of the Royal Society, FRS (3 November 1828 – 9 March 1917) was an England, English clergyman and zoologist. He was a keen arachnologist who described and named more than 900 species of spider. Life and wor ...

described what he considered to be a different although closely related species. He decided that was not a ''

Theridion ''Theridion'' is a genus of tangle-web spiders with a worldwide distribution. Notable species are the Hawaiian happy face spider (''T. grallator''), named for the iconic symbol on its abdomen, and '' T. nigroannulatum'', one of few spi ...

'', and placed it in a new genus, ''Theridiosoma'', as ''T. argenteolum''.

Eugène Simon Eugène Louis Simon (; 30 April 1848 – 17 November 1924) was a French naturalist who worked particularly on insects and spiders, but also on birds and plants. He is by far the most prolific spider taxonomist in history, describing over 4, ...

in 1881 recognized that Koch's and Pickard-Cambridge's species were the same and united them under the current name ''Theridiosoma gemmosum''.

Distribution and habitat

''Theridiosoma gemmosum'' has a

distribution, i.e. it is found throughout the northern and central parts of the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. It is described as "rare" in northern Europe, including

Great Britain Great Britain is an island in the North Atlantic Ocean off the northwest coast of continental Europe. With an area of , it is the largest of the British Isles, the largest European island and the ninth-largest island in the world. It is ...

and

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

. It is usually found in damp habitats, among low-growing vegetation.

References

{{Taxonbar, from=Q244301 Holarctic spiders Theridiosomatidae Spiders described in 1877