Platybunus

Belongs within: Phalangiidae.

Platybunus is a genus of phalangiid harvestmen found in central and south-east Europe. Members of this genus have a conspicuously large eyemound and long spines on the pedipalp (Martens 1978).

Platybunus: the wide-eyed harvestmen of Europe

Published 8 May 2022

The western Palaearctic region (that is, Europe and the immediately adjacent parts of Asia and northern Africa) is home to a diverse and distinctive fauna of harvestmen. Among the various genera unique to this part of the world are the forest- and mountain-dwellers of the genus Platybunus.

Platybunus species are moderate-sized long-legged harvestmen of the family Phalangiidae, the central body in larger individuals being about eight millimetres long (Martens 1978). Their most characteristic feature is a relatively large eye-mound, distinctly wider than long and occupying a large section of the anterior carapace. As with other European phalangiids, they eye-mound is ornamented with a row of denticles each side though the body lacks denticles over the remainder of the dorsum. The body is often comparatively slender, tapering towards the rear (particularly in males), and is marked on the dorsum by a darker median band. The pedipalps have a pair of well-developed setose apophyses on the inner distal ends of the patella and tibia, and a series of long spine-like tubercles on the underside of the femur. These tubercles presumably function in the capture of prey, forming a basket that can be closed around the harvestman’s victims. External sexual dimorphism in Platybunus is fairly minimal though females are overall larger and fatter. The penis is notably long and slender with a relatively small glans, offset from the shaft by a more or less marked constriction.

Martens (1978) recognises four species of Platybunus found in higher altitude regions of central Europe with the species P. bucephalus and P. pinetorum occupying much of the genus’ range. Platybunus bucephalus may be distinguished from P. pinetorum by, among other features, its relatively shorter legs. Platybunus pallidus is endemic to the Carpathians, and the tiny P. alpinorelictus inhabits the Garda Mountains of northern Italy. Another species, P. anatolicus, was described from Turkey by Roewer (1956)*. In general, Platybunus species inhabit alpine and subalpine forests, being found among the herbaceous undergrowth, under bark or on rock faces. Where their ranges overlap, P. bucephalus is more accustomed to extending beyond the forest margins than P. pinetorum and may be found above the tree-line. In recent years, the range of P. pinetorum has extended northwards, being first recorded from the UK in 2010 and Sweden in 2015 (Fritzén et al. 2015). At least some populations of P. pinetorum are capable of reproducing parthenogenetically and this may have played a part in its spread.

*Platybunus mirus was described by Loman (1892) on the basis of two male specimens that supposedly came from Sumatra. Though the identity of this species has never been resolved (Loman’s illustration of the penis is at least suggestive of a true Platybunus), the claimed locality seems almost certain to be an error of some kind.

The internal classification of the Phalangiidae remains in need of further investigation. Platybunus has been recognised by some authors as forming a subfamily Platybuninae with a cluster of other western Palaearctic genera bearing similar ventrally spined pedipalps (Zhang & Zhang 2012). However, other authors have not separated this group from the subfamily Phalangiinae. The platybunines may represent a phylogenetically coherent grouping, or their shared features may reflect adaptations to a similar life style. The genital morphology of Platybunus is recognisably distinct from that of other platybunines which may argue against any relationship (Martens 1978). On the other hand, platybunines might possibly be distinguished from phalangiines by the chemical composition of their repugnatorial gland secretions (Raspotnig et al. 2015). A formal analysis of the family’s evolution would be a welcome advance.

Systematics of Platybunus

Characters (from Martens 1978): Body of male commonly caudad bluntly tapered caudad, dorso-ventrally flattened. Supracheliceral lamellae unarmed. Tuber oculorum conspicuously large, wider than long, medially grooved, with lateral denticles, about one-quarter to half its length from front margin of cephalothorax. Pedipalp robust and powerful; femur, tibia and tarsus with long spines (fewer on tibia and tarsus); patella and tibia each with conspicuous medio-distal apophysis, form of patellar apophysis usually varying between sexes. Truncus penis extremely long and narrow, with nearly parallel margins, basally slightly enlarged, either dorsally or ventrally flat, otherwise convex; muscles in basal third to basal half. Glans elongate spindle-shaped; sense bristles large, in bright socket, near base of glans. Receptaculum seminis mostly thick-walled.

<==Platybunus Koch 1839K18 [incl. Platylophus Koch 1839 non Swainson 1832C92]
    |--*P. bucephalus (Koch 1835)C92 (see below for synonymy)
    |--‘Platylophus’ affinis Koch 1871 (n. d.)R23
    |--P. alpinorelictus Martens 1978M78
    |--P. arbuteus Simon 1879 (n. d.)D04
    |--P. hadzii Kratochvíl 1935N05
    |--‘Platylophus’ heegeri Kollar in Rossi in Haidingers 1847 (n. d.) [=P. dalmatinum ms, P. hugeri (l. c.)]R23
    |--P. hypanicus Šilhavý 1966K14
    |--P. incanus Koch 1839 (n. d.) [=Phalangium incanum, Platylophus incanus]R23
    |--‘Platylophus’ leucophthalmus Koch 1871 (n. d.)R23
    |--P. mirus Loman 1892R23
    |--P. nigrovittatus Simon 1879D04
    |--P. pallidus Šilhavý 1938M78
    |--P. pinetorum (Koch 1839)N05 (see below for synonymy)
    |--P. placidus Simon 1879D04
    |--P. strigosus (Koch 1867)N05 [=Platylophus strigosusR23, Metaplatybunus strigosusR23]
    `--P. uncatus (Hermann 1804) (n. d.) [=Phalangium uncatum]R23
Nomen nudum: Platylophus biramosus Kollar in Doleschall 1852R23

*Platybunus bucephalus (Koch 1835)^C92 [=Opilio bucephalus^D04, Platybunus budephalus (l. c.)^R23, Platylophus bucephalus^D04; incl. Platybunus eques Simon 1881^D04, Platybunus exiguus Roewer 1956^D04, Platylophus montanus Koch 1867^D04, Opilio rufipes Koch 1836^D04, Platybunus rufipes^D04, *Platylophus rufipes^C92]

Platybunus pinetorum (Koch 1839)^N05 [=Platylophus pinetorum^D04; incl. Platybunus agilis Koch 1861^D04, Platylophus alpestris Koch 1839^D04, Platybunus cirdeii Avram 1964^D04]

*Type species of generic name indicated

References

[C92] Crawford, R. L. 1992. Catalogue of the genera and type species of the harvestman superfamily Phalangioidea (Arachnida). Burke Museum Contributions in Anthropology and Natural History 8: 1–60.

[D04] Delfosse, E. 2004. Catalogue préliminaire des Opilions de France métropolitaine (Arachnida Opiliones). Bulletin de Phyllie 20: 34–58.

Fritzén, N. R., V. Rinne, M. Sunhede, A. Uddström, S. Van de Poel & P. De Smedt. 2015. Platybunus pinetorum (Arachnida, Opiliones) new to Sweden. Memoranda Soc. Fauna Flora Fennica 91: 37–40.

[K14] Kurt, K. 2014. Updated checklist of harvestmen (Arachnida: Opiliones) in Turkey. Arch. Biol. Sci. 66 (4): 1617–1631.

[K18] Kury, A. B. 2018. Familial nomina in harvestmen (Arachnida, Opiliones). Bionomina 13: 1–27.

Loman, J. C. C. 1892. Opilioniden von Sumatra, Java und Flores. In: M. Weber (ed.) Zoologische Ergebnisse einer Reise in Niederländisch Ost-Indien vol. 3 pp. 1–26, pl. 1. E. J. Brill: Leiden.

[M78] Martens, J. 1978. Spinnentiere, Arachnida: Weberknechte, Opiliones. Gustav Fischer Verlag: Jena.

[N05] Novak, T. 2005. An overview of harvestmen (Arachnida: Opiliones) in Bosnia and Herzegovina. Natura Croatica 14 (4): 301–350.

Raspotnig, G., M. Schaider, P. Föttinger, V. Leutgeb & C. Komposch. 2015. Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis. Chemoecology 25: 63–72.

[R23] Roewer, C.-F. 1923. Die Weberknechte der Erde: Systematische Bearbeitung der bisher bekannnten Opiliones. Gustav Fischer: Jena.

Roewer, C. F. 1956. Über Phalangiinae (Phalangiidae, Opiliones Palpatores). (Weitere Weberknechte XIX). Senckenbergiana Biologica 37 (3–4): 247–318.

Zhang, C., & F. Zhang. 2012. On the subfamilial assignment of Platybunoides (Opiliones: Eupnoi: Phalangiidae), with the description of a new species from China. Zootaxa 3190: 47–55.