Exechocentrus

Exechocentrus is a genus of Madagascan orb-weaver spiders (family Araneidae) first described by Eugène Simon in 1889.[1][2] 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.

Exechocentrus
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Araneomorphae
Family: Araneidae
Subfamily: Cyrtarachninae s.l.
Genus: Exechocentrus
Simon, 1889[1]
Type species
E. lancearius
Simon, 1889
Species

See text.

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. One is centrally placed and extends forwards; three are more-or-less upright. The total body length is 3.9–5.4 mm (1⁄8–3⁄16 in). The cephalothorax is yellowish-white with brown lines radiating from the fovea 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 has a strongly hardened (sclerotized) lip. The spermathecae are large and ovoid, with short narrow copulatory ducts.[3]

Taxonomy

The genus Exechocentrus was erected by Eugène Simon in 1889 for the species Exechocentrus lancearius, 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.[3]

A 2020 molecular phylogenetic analysis placed the genus in the informal group mastophorines of a broadly defined subfamily Cyrtarachninae s.l.[4]

Species

As of April 2019 it contained only two species, both found in Madagascar.[1]

Prey capture

The probable relationship of the genus Exechocentrus to the bolas spiders placed in the tribe Mastophorini (Mastophoreae) had been noted by Emerit in 2000, who suggested that it might also capture prey with a bolas. 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.[3] The relationship to other bolas spiders was confirmed by a molecular phylogenetic analysis in 2020.[4]

References
  1. "Gen. Exechocentrus Simon, 1889". World Spider Catalog. Natural History Museum Bern. Retrieved 2019-05-13.
  2. Simon, E. (1889). "Etudes arachnologiques. 21e Mémoire. XXXI. Descriptions d'espèces et the genres nouveaux de Madagascar et de Mayotte". Annales de la Société Entomologique de France. 8 (6): 223–236.
  3. Scharff, Nikolaj & Hormiga, Gustavo (2012). "First evidence of aggressive chemical mimicry in the Malagasy orb weaving spider Exechocentrus lancearius Simon, 1889 (Arachnida: Araneae: Araneidae) and description of a second species in the genus" (PDF). Arthropod Systematics & Phylogeny. 70 (2): 107–118. Retrieved 2021-01-17.
  4. Scharff, N.; Coddington, J.A.; Blackledge, Todd A.; Agnarsson, Ingi; Framenau, Volker W.; Szűts, Tamás; Hayashii, Cheryl Y. & Dimitrov, Dimitar (2020). "Phylogeny of the orb‐weaving spider family Araneidae (Araneae: Araneoidea)". Cladistics. 36: 1–21. doi:10.1111/cla.12382. hdl:1956/22200.
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