''Exechocentrus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of Madagascan

orb-weaver spider Orb-weaver spiders are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields, and forests. The English word "orb" can mean "circular", hence the English name ...

s (family Araneidae) first described by

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 1889. It is a bolas-using spider, capturing its prey with one or more sticky drops at the end of a single line of silk rather than in a web.

Description

Males of the genus are unknown. Females can be distinguished from all other known members of the family Araneidae by the spine-like projections on 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 ''ceph ...

. One is centrally placed and extends forwards; three are more-or-less upright. The total body length is . The cephalothorax is yellowish-white with brown lines radiating from the

fovea Fovea () (Latin for "pit"; plural foveae ) is a term in anatomy. It refers to a pit or depression in a structure. Human anatomy * Fovea centralis of the retina * Fovea buccalis or Dimple * Fovea of the femoral head *Trochlear fovea of the f ...

and is about as wide as it is long. The legs are pale yellowish-white with dark brown markings. The abdomen is off white and almost heart-shaped from above. The

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. ...

has a strongly hardened (sclerotized) lip. The

spermathecae The spermatheca (pronounced plural: spermathecae ), also called receptaculum seminis (plural: receptacula seminis), is an organ of the female reproductive tract in insects, e.g. ants, bees, some molluscs, oligochaeta worms and certain other ...

are large and ovoid, with short narrow

copulatory ducts Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal pen ...

Taxonomy

The genus ''Exechocentrus'' was erected by

in 1889 for the species ''

Exechocentrus lancearius ''Exechocentrus lancearius'' is a species of spider in the orb-weaver spider family Araneidae, found only in Madagascar. It was initially described from a partial specimen of an adult female. The first description of a complete specimen and its ...

'', which was described based on a specimen lacking an abdomen. No complete adult specimen was known until a collection in 2000. ''E. lancearius'' remained the only species in the genus until 2009, when an adult female was collected that was discovered to belong to a different species of ''Exechocentrus'', which was described as '' Exechocentrus madilina'' in 2012. The two species are distinguished by features of the abdomen, so Simon's original type specimen cannot be assigned with certainty to either of them. A 2020

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 ...

analysis placed the genus in the informal group mastophorines of a broadly defined subfamily Cyrtarachninae ''s.l.''

Species

it contained only two species, both found in

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Africa ...

. *''

'' Simon, 1889 – Madagascar *'' Exechocentrus madilina'' Scharff & Hormiga, 2012 – Madagascar

Prey capture

The probable relationship of the genus ''Exechocentrus'' to the

bolas spider A bolas spider is a member of the orb-weaver spider (family Araneidae) that, instead of spinning a typical orb web, hunts by using one or more sticky "capture blobs" on the end of a silk line, known as a "bolas". By swinging the bolas at flying ...

s placed in the tribe Mastophorini (Mastophoreae) had been noted by Emerit in 2000, who suggested that it might also capture prey with a

bolas Bolas or bolases (singular bola; from Spanish and Portuguese ''bola'', "ball", also known as a ''boleadora'' or ''boleadeira'') is a type of throwing weapon made of weights on the ends of interconnected cords, used to capture animals by ent ...

. However, foraging behaviour was not observed until 2009, when an adult female ''Exechocentrus lancearius'' was seen to use a bolas with two droplets. The bolas was manipulated with the spider's second pair of legs and swung in a horizontal direction. The relationship to other bolas spiders was confirmed by a

analysis in 2020.

References

{{Taxonbar, from=Q3061879 Araneidae Araneomorphae genera Spiders of Madagascar Taxa named by Eugène Simon