''Exechocentrus lancearius'' 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

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

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 prey-catching behaviour was published in 2012. ''E. lancearius'' is a

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 flyin ...

. Rather than using a web, adult females catch their prey by using a line with one or two sticky drops (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 entan ...

") which they swing.

Description

The

neotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

female was described by Scharff and Hormiga in 2012. The total length of the body is 3.9 mm. The cephalothorax is about 2.0 mm long and wide, and the abdomen 2.7 mm long and 3.9 mm wide. (The abdomen overlaps the cephalothorax.) The cephalothorax is pear-shaped and has four spine-like projections, one pointing forwards and three in a triangle behind it. The carapace is yellowish white with a white central stripe and dark brown markings. The

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...

is blackish brown. The legs are yellowish white with orange brown markings. The first leg is the longest, being 12.4 mm from the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

to the tarsus. The abdomen is somewhat heart-shaped with two long projections at the rear. It is whitish on the upper surface with dark sigilla, and yellowish brown on the lower surface with a broad black band in the centre. 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 projecting hardened U-shaped lip. The male is unknown.

Taxonomy

''Exechocentrus lancearius'' was first described by Eugène Simon in 1889. It was the only species in his new genus ''

Exechocentrus ''Exechocentrus'' is a genus of Madagascan orb-weaver spiders (family Araneidae) first described by Eugène Simon 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 ...

''. Simon's description was based on a specimen lacking an abdomen; no complete adult specimen was known until one was collected in 2000. Since ''E. lancearius'' can be distinguished from '' E. madilina'' only by features of the abdomen, Simon's specimen cannot be assigned to either species with certainty, and in 2012, a new

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

was designated. A 2020 molecular phylogenetic analysis placed the genus in the informal group mastophorines of a broadly defined subfamily

Cyrtarachninae Cyrtarachninae is a subfamily of spiders in the family Araneidae (orb-weaver spiders, araneids). The group has been circumscribed in several different ways. It originated as the group Cyrtarachneae, described by Eugène Simon in 1892. The group w ...

''s.l.''

Prey capture

The relationship of ''Exechocentrus lancearius'' (then the only species in the genus) to the

s placed in the tribe Mastophoreae had been noted by Emerit in 2000. Rather than a web, bolas spiders capture prey using a line with one or more sticky drops, which they swing at prey. However, the foraging behaviour of ''E. lancearius'' was not known until 2009 when a female using a bolas was observed shortly after sunset. It had produced a horizontal line of silk underneath a leaf about 1.5 m above the ground. It had also produced a bolas attached to the horizontal line by one end. The bolas was about 26 mm long, with one sticky droplet at the end furthest from the attachment and another about 4 mm above it. The bolas was manipulated with the second pair of legs and swung in a horizontal direction. No prey were seen to be caught during the period of observation.

References

Araneidae Spiders of Madagascar Endemic fauna of Madagascar Spiders described in 1889 Taxa named by Eugène Simon {{Araneidae-stub