The Palpimanoidea or palpimanoids, also known as assassin spiders, are a group of araneomorph spiders, originally treated as a superfamily. As with many such groups, its

circumscription Circumscription may refer to: * Circumscribed circle * Circumscription (logic) *Circumscription (taxonomy) * Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthr ...

has varied. , the following five families were included: * Archaeidae * Huttoniidae * Mecysmaucheniidae * Palpimanidae * Stenochilidae Many palpimanoids specialize in preying on other spiders, hence the name "assassin spiders". They have various adaptations for catching prey, including enlarged spade-like front legs, and heads raised up on a "neck" with long

chelicerae The chelicerae () are the arthropod mouthparts, mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated ...

("jaws"). Fossils suggest that the group was once widespread, but most species are now found in the Southern Hemisphere. Morphological studies support the

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

of the group, although molecular studies have produced different results.

Description

Many palpimanoids, particularly members of the families Archaeidae, Huttoniidae and Stenochilidae, specialize in preying on other spiders, hence the description "assassin spiders". They enter the retreats and webs of other spiders and seize them. Members of the families Huttoniidae, Palpimanidae and Stenochilidae have extensive scopulae on the sides of their often enlarged front legs, which enable them to both seize and manipulate prey. Members of the family Archaeidae have much smaller scopulae, but have a highly modified

prosoma 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 ...

(cephalothorax), in which a long narrow "neck" separates a "head" portion from the rest of the prosoma. The long neck is matched by long

. Members of the Mecysmaucheniidae also have an elongated prosoma and chelicerae, although less so than archaeids. When hunting prey, mecysmaucheniids hold their chelicerae widely open. Long, forward directed hairs (setae) appear to act as triggers; when these are touched by prey, the chelicerae rapidly snap shut, enabling mecysmaucheniids to catch fast-moving prey, such as

springtail Springtails (class Collembola) form the largest of the three lineages of modern Hexapoda, hexapods that are no longer considered insects. Although the three lineages are sometimes grouped together in a class called Entognatha because they have in ...

s. Zephyrarchaea grayi anatomy.jpg, '' Zephyrarchaea grayi'' (Archaeidae), showing the "neck" and long chelicerae (bar = 1 mm) Zearchaea clypeata female.jpg, '' Zearchaea clypeata'' (Mecysmaucheniidae), showing the less long "neck" and chelicerae Boagrius sp.jpg, '' Boagrius'' sp. (Palpimanidae), showing the enlarged front legs (bar = 1 mm)

Phylogeny

In 1984, Raymond R. Forster and

Norman I. Platnick Norman Ira Platnick (December 30, 1951 – April 8, 2020) was an American biological systematist and Arachnology, arachnologist. At the time of his death, he was a professor emeritus of the American Museum of Natural History#Richard Gilder Gradua ...

proposed that some groups previously considered araneoid actually belonged in the distantly related Palpimanoidea, including the then families Holarchaeidae, Micropholcommatidae, Mimetidae and Pararchaeidae. Subsequent phylogenetic studies have rejected this proposal, firmly placing them in Araneoidea. Studies published in 2012 and 2013, using morphological, molecular and fossil evidence, agreed that Palpimanoidea is monophyletic. Molecular data suggested the following relationship between the five families comprising the Palpimanoidea, although three of the families were represented by only one species each: Using only morphological data produced a different arrangement of the families: A large

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study, first published online in 2016, grouped the five families in the same way, but suggested that the Palpimanoidea, together with part of the non-monophyletic

Leptonetidae Leptonetidae is a family of small spiders adapted to live in dark and moist places such as caves. The family is relatively primitive having diverged around the Middle Jurassic period. They were first described by Eugène Simon in 1890. Distingu ...

, were a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group basal to the large

Entelegynae The Entelegynae or entelegynes are a subgroup of araneomorph spiders, the largest of the two main groups into which the araneomorphs were traditionally divided. Females have a genital plate ( epigynum) and a "flow through" fertilization system; ...

clade: Nevertheless, the authors preferred to accept the earlier conclusion based on multiple lines of evidence that the Palpimanoidea are a monophyletic group. Although the morphological data suggests that the two families with "necks" in the prosoma, Archaeidae and Mecysmaucheniidae, are sisters, molecular data suggests otherwise. It is now believed that the elongated and elevated "neck" has evolved independently in these two families, as well as in the more distantly related Malkaridae (Pararchaeidae).

Distribution

The Palpimanoidea are mainly found in the Southern Hemisphere. Archaeidae, Huttoniidae and Mecysmaucheniidae have a

Gondwana Gondwana ( ; ) was a large landmass, sometimes referred to as a supercontinent. The remnants of Gondwana make up around two-thirds of today's continental area, including South America, Africa, Antarctica, Australia (continent), Australia, Zea ...

n distribution, with species native to South America, South Africa, Madagascar, Australia and New Zealand. The Stenochilidae are found in South-east Asia. Only the Palpimanidae cross into 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 by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...

, with a few species reaching Central Asia and China. Palpimanoids were once more widely distributed; thus 12 fossil genera of Archaeidae have been found in the Northern Hemisphere.

References

{{Taxonbar, from=Q54905 Araneomorphae Arachnid superfamilies