Ischnocolinae

The Ischnocolinae are a problematic subfamily of tarantulas (family Theraphosidae). In 1892, Eugène Simon based the group, which he noted was only weakly homogeneous, on the presence of divided tarsal scopulae. This feature was later considered to be plesiomorphic (i.e. potentially inherited from an ancestor by multiple descendant groups), and both morphological and molecular phylogenetic studies have shown that, as traditionally circumscribed, the subfamily is not monophyletic. A much more narrowly defined Ischnocolinae sensu stricto was proposed in 2014. One of the authors of that proposal subsequently said that no further taxonomic changes should be considered until there had been a more comprehensive sampling of the subfamily. As of January 2021, the status of the Ischnocolinae remains unresolved.

Ischnocolinae
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Infraorder: Mygalomorphae
Family: Theraphosidae
Subfamily: Ischnocolinae
Simon, 1892
Genera

See text.

Taxonomy

In 1872, Anton Ausserer erected the genus Ischnocolus. Ausserer used the division of the scopulae on the tarsi of the third and fourth legs as a key characteristic.[1] The subfamily Ischnocolinae was first described (as the group Ischnocoleae) by Eugène Simon in 1892. Following Ausserer's characterization of the genus, Simon used the divided tarsal scopulae as the defining characteristic of the group. However, Simon noted that "à part ce caractère .. les Ischnocoleae n'ont guère de particularités communes et ils forment un ensemble peu homogène" (apart from this character .. the Ischnocoleae have hardly any common characteristics and they form a weakly homogeneous set).[2] Doubts were expressed early on as to the validity of the divided tarsal scopulae as a defining characteristic. In 1895, R.I. Pocock said that it could be "nothing but a sign of immaturity". Young spiders have only fine hairs (setae) rather than scopulae. In successive moults, scopulae replace the setae in stages, so divisions at first present may disappear when the scopulae are complete at full maturity.[3] In spite of these concerns, genera were continually added to the subfamily, so that in 1986, for example, Andrew M. Smith said the subfamily included 49 genera, although he regarded it as "ripe for sweeping revision".[4] In his 1985 monograph on the Mygalomorphae, Robert Raven considered the divided tarsal scopulae to be a plesiomorphic character and the Ischnocolinae to be non-monophyletic, treating it as Theraphosidae incertae sedis. His key to the subfamilies of the Theraphosidae split genera that had been placed in the subfamily among three informal groups.[5]

In 2014, a molecular phylogenetic study was published that confirmed the non-monophyly of Ischnocolinae when broadly defined. A small number of genera could be retained in much reduced subfamily, Ischnocolinae sensu stricto, and another group were placed in a new subfamily, Schismatothelinae. The remaining genera were distributed across the theraphosid phylogeny.[6] This result has been confirmed by other studies, one of which also suggested that the newly defined subfamily Schismatothelinae was not monophyletic.[7]

In 2020, Guadanucci summarized the status of the subfamily at that time. Most of the members that had been studied were scattered across the family tree of the Theraphosidae. Guadanucci considered that no further taxonomic changes should be considered until there had been a comprehensive sampling of the subfamily in a molecular phylogenetic study.[8]

Genera

According to Guadanucci in 2014, a much reduced subfamily, Ischnocolinae sensu stricto, was monophyletic.[6] It included species from five genera:

Species in several genera were placed in the newly created Schismatothelinae.[6] Subsequently some species were transferred to other genera.[9][10]

  • Euthycaelus (E. colonica, originally treated as Holothele colonica, plus an unidentified related species)
  • Guyruita (G. cerrado, G. atlantica)
  • Neoholothele (N. incei, originally treated as Holothele incei, plus an unidentified related species)
  • Schismatothele (S. lineata, S. modesta, originally treated as Hemiercus modestus)
  • Sickius (S. longibulbi)

Genera suggested to be excluded from the subfamily Ischnocolinae as they were unresolved across the phylogeny include:[6]

Also in 2014, Mirza, Sanap & Bhosale further revised some Indian taxa associated with the Ischnocolinae, described the new genus Sahydroaraneus, and treated them in the subfamily Eumenophorinae.[11]

References
  1. Ausserer, A. (1871). "Beiträge zur Kenntniss der Arachniden-Familie der Territelariae Thorell (Mygalidae Autor)". Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien. 21: 117–224. "Scopula an Tarsus III und IV sehr deutlich getheilt", p. 127.
  2. Simon, E. (1892). "1. Ischnocoleae". Histoire naturelle des araignées. Vol. 1(1) (2nd ed.). Paris: Roret. p. 133ff. doi:10.5962/bhl.title.51973.
  3. Pocock, R.I. (1895). "Notes on the identity of some of the types of Mygalomorphae in the collection of the British Museum". Annals and Magazine of Natural History (Series 6). 16: 223–230. Retrieved 2021-01-28. p. 225.
  4. Smith, Andrew M. (1986). The Tarantula : Classification and Identification Guide. London: Fitzgerald Publishing. ISBN 978-0-9510939-0-0. p. 70.
  5. Raven, Robert J. (1985). "The spider infraorder Mygalomorphae (Araneae): cladistics and systematics". Bulletin of the American Natural History Museum. 182. Retrieved 2016-01-18. p. 116ff.
  6. Guadanucci, J.P.L. (2014). "Theraphosidae phylogeny: relationships of the 'Ischnocolinae' genera (Araneae, Mygalomorphae)". Zoologica Scripta. 43 (5): 508–518. doi:10.1111/zsc.12065.
  7. Foley, Saoirse; Lüddecke, Tim; Cheng, Dong-Qiang; Krehenwinkel, Henrik; Künzel, Sven; Longhorn, Stuart J.; Wendt, Ingo; von Wirth, Volker; Tänzler, Rene; Vences, Miguel & Piel, William H. (2019). "Tarantula phylogenomics: A robust phylogeny of deep theraphosid clades inferred from transcriptome data sheds light on the prickly issue of urticating setae evolution". Molecular Phylogenetics and Evolution. 140: 106573. doi:10.1016/j.ympev.2019.106573.
  8. Guadanucci, J.P.L. (2020). "Ischnocolinae and Schismatothelinae". In Pérez-Miles, F. (ed.). New World Tarantulas. Zoological Monographs, vol 6. Cham: Springer International Publishing. doi:10.1007/978-3-030-48644-0_3. ISBN 978-3-030-48643-3.
  9. Guadanucci, J.P.L. & Weinmann, D. (2014). "The spider genera Euthycaelus Simon and Schismatothele Karsch (Mygalomorphae, Theraphosidae)". Zootaxa. 3795 (3): 275–288. doi:10.11646/zootaxa.3795.3.3.
  10. Guadanucci, J.P.L. & Weinmann, D. (2015). "Description of Neoholothele gen. nov. (Araneae, Theraphosidae, Schismatothelinae)". Studies on Neotropical Fauna and Environment. 50 (3): 221–228. doi:10.1080/01650521.2015.1110309. hdl:11449/161205.
  11. Mirza, Z.A.; Sanap, R.V. & Bhosale, H. (2014). "Preliminary review of Indian Eumenophorinae (Araneae: Theraphosidae) with description of a new genus and five new species from the Western Ghats". PLoS One. 9 (2): e87928. doi:10.1371/journal.pone.0087928.


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