Tychus

Tychus niger, copyright Pierre Bornand.

Belongs within: Pselaphinae.

The little tyke that is Tychus
Published 15 December 2014
Male (left) and female of Tychus niger, copyright Lech Borowiec.

Another brief beetle post for today. The species in the image above is the type species of Tychus, a genus of about 150 species of pselaphine beetles found in Eurasia and North America. Chandler (1988) regarded the North American species as a separate genus Hesperotychus but Kurbatov & Sabella (2008) felt that the differences between species from the two continents were not enough to warrant separation. There’s probably still some work to be done here.

Like many other pselaphines, most of the work on Tychus has focused on the morphology of the various species, with relatively little having been said about its life habits. Heer (1841) described the habitat of T. niger as ‘sub lapidibus et in graminosis’ which I believe means ‘under stones and among grass’, and Kurbatov & Sabella (2008) recorded collecting a specimen of Atychodea pilicollis, a related species, in damp sand. The large, broad-ended palps (the appendages on the head behind the antennae) of Tychus species suggests that they are probably micropredators. Like most pselaphines, the small size of Tychus species means that they generally escape observation.

Tychus is the largest genus in the pselaphine tribe Tychini. Tychins are most diverse in the Holarctic region, with only a very few species found in southern and south-east Asia. Chandler (1988) characterised the Tychini by the shape of the third segment of the palp, which is invariably longer than wide, and by the antennae usually being inserted close together on a narrow rostrum, though this varies a lot in distinctiveness between species. Kurbatov & Sabella (2008) also identified a number of other features representing possible synapomorphies of the Tychini, and suggested that the Oriental genera Atychodea and Amorphodea represent the sister taxon of the remaining Holarctic genera. The genera of Tychini are all fairly similar in appearance; notable distinguishing features of Tychus include an asymmetrical aedeagus (the intromittent organ in the male genitalia) and the arrangement of foveae (hollows) on the elytra and sternites. Males of Tychus often have one of the antennal segments modified as in the male of T. niger shown above, with a median segment noticeably thicker and broader than those on either side. The purpose of this enlarged segment, as with so many other features of pselaphines, seems to be unknown.

Systematics of Tychus
<==Tychus Leach 1817R04a
    |--T. algericus Guilleb. 1893 [incl. T. castaneus Saulcy in Raffray 1904 (n. n.) non Aubé 1844, T. tuniseus Pic 1901]R04a
    |--T. angulifer Reitter 1881R04a
    |--T. anophthalmus Reitter 1881R04a
    |--T. armatus Saulcy 1870R04a
    |--T. armeniacus Saulcy 1878R04a
    |--T. bispina Saulcy in Raffray 1904R04a
    |--T. bosnicus Ganglbauer 1897R04a
    |--T. brunneus Motsch. 1851 [incl. T. caucasicus Saulcy 1878]R04a
    |--T. bryaxioides Guilleb. 1893 (see below for synonymy)R04a
    |--T. castaneus Aubé 1844R04a
    |--T. caudatus Reitter 1884R04a
    |--T. cognatus Leconte 1874 [incl. T. bipuncticeps Casey 1887]R04a
    |--T. dalmatinus Reitter 1880R04a
    |--T. dentifrons Reitter 1881R04a
    |--T. florentinus Reitt. 1884R04a
    |--T. fournieri Saulcy 1864 [incl. T. fournieri var. olbiensis Guilleb. 1888]R04a
    |--T. ganglbaueri Apfelbeck 1897R04a
    |--T. gibbiventris Reitter 1884R04a
    |--T. grandiceps Reitter 1881R04a
    |--T. guillebeaui Raffray 1904 [=T. colchicus Guilleb. 1878 non Saulcy 1878]R04a
    |--T. hexagonus Casey 1897R04a
    |--T. hirtulus Reitter 1880R04a
    |--T. ibericus Motsch. 1835 (see below for synonymy)R04a
    |--T. integer Reitter 1881R04a
    |--T. jacquelini Boieldieu 1859 [incl. T. cornutus Croiss. 1893]R04a
    |--T. lederi Saulcy 1878R04a
    |--T. lenkoranus Reitter 1881R04a
    |--T. mendax Kiesenw. 1858R04a
    |--T. microphthalmus Brendel 1893R04a
    |--T. miles Saulcy 1870R04a
    |--T. minor [incl. T. testaceus Casey 1884 non Schaufuss 1877]R04a
    |--T. niger Paykull 1789 (see below for synonymy)R04a
    |--T. nodicornis Reitter 1884R04a
    |--T. nodifer Reitter 1884R04a
    |--T. pocahontasR04a
    |--T. puberulusR04a
    |--T. pullus Kiesenw. 1858R04a
    |--T. rufopictus Reitter 1881R04a
    |--T. rufus Motsch. 1851 (see below for synonymy)R04a
    |--T. serbicus Reitter 1884R04a
    |--T. sonomae Casey 1887R04a
    |--T. spiculifer Casey 1893R04a
    |--T. sternalis Raffray 1904R04a
    |--T. tasmaniae Schauf. 1886M96
    |--T. tenellusR04a
    |--T. tenuicornis Baudi 1869R04a
    |--T. tuberculatus Aubé 1844R04a
    `--T. verticalis Casey 1893R04a
Nomina nuda: Tychus angusticollis Motschulsky 1856R04b
             Tychus dilatatus Motschulsky 1851R04b
             Tychus nigripennis Motschulsky 1856R04b
             Tychus pilosus Motschulsky 1855R04b
             Tychus ruber Motschulsky 1845R04b
             Tychus serricornis Motschulsky 1845R04b

Tychus bryaxioides Guilleb. 1893 [incl. T. auriculatus (n. n.), T. auverti Croissandeau 1893, T. koziorowiczi Croissandeau 1893, T. bryaxioides var. pici Croissandeau 1893, T. bryaxioides var. poupillieri Raffray 1904, T. bryaxioides var. raffrayi Peyerimhoff 1904]R04a

Tychus ibericus Motsch. 1835 [incl. T. ibericus var. corsicus Reitter 1881, T. ibericus var. creticus Reitter 1885, T. erythropterus Schmidt 1838, T. ibericus var. monilicornis Reitt. 1880, T. ibericus var. mutinensis Reitter 1884, T. rufopictus Guilleb. 1888 (preoc.), T. striola Guilleb. 1888]R04a

Tychus niger Paykull 1789 [incl. T. niger var. colchicus Saulcy 1878, T. niger var. dichrous Schmidt 1836, T. nodicornis Beck non Reitter 1884, T. tauricus Motsch. 1851]R04a

Tychus rufus Motsch. 1851 [incl. T. rufus var. morio Reitter 1881, T. myops Kiesenw. 1858, T. rufus var. puncticollis Reitter 1887]R04a

*Type species of generic name indicated

References

Chandler, D. S. 1988. A cladistic analysis of the world genera of Tychini (Coleoptera: Pselaphidae). Transactions of the American Entomological Society 114 (2): 147–165.

Heer, O. 1841. Fauna Coleopterorum Helvetica pars 1. Impensis Orelii, Fuesslini et Sociorum: Turici.

Kurbatov, S. A., & G. Sabella. 2008. Revision of the genus Atychodea Reitter with a consideration of the relationships in the tribe Tychini (Coleoptera, Staphylinidae, Pselaphinae). Transactions of the American Entomological Society 134 (1–2): 23–68.

[M96] Masters, G. 1896. Catalogue of the described Coleoptera of Australia. Supplement, part II. Dytiscidae, Gyrinidae, Hydrophyllidae, Staphylinidae, Pselaphidae, Paussidae, Silphidae, Scaphididae, Histeridae, Phalacridae, Nitidulidae, Trogositidae, Colydiidae, Cucujidae, Cryptophagidae, Lathridiidae, Mycetophagidae, Dermestidae, Byrrhidae, Parnidae, Heteroceridae. Proceedings of the Linnean Society of New South Wales 21 (Suppl.): 695–754.

[R04a] Raffray, A. 1904a. Genera et catalogue des psélaphides [part II]. Annales de la Société Entomologique de France 73: 1–400.

[R04b] Raffray, A. 1904b. Genera et catalogue des psélaphides [part III]. Annales de la Société Entomologique de France 73: 401–476, pls 1–3.

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