Unixenus mjoebergi (Verhoeff, 1924)

Short, Megan & Huynh, Cuong, 2011, The genus Unixenus Jones, 1944 (Diplopoda, Penicillata, Polyxenida) in Australia, ZooKeys 156, pp. 105-122 : 111-113

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Unixenus mjoebergi (Verhoeff, 1924)


Unixenus mjoebergi (Verhoeff, 1924) Figs 1B3A, 3B, 3E

Monographis mjoebergi Verhoeff, 1924: 38.

Unixenus mjoebergi Nguyen Duy-Jacquemin and Condé, 1967: 73, figs 11, 12.

Material examined.

Slide preparations were made of adults from the following collections: Barrow Island, WA, 20°47'38"S, 115°27'24"E, sites 17 (2 suction samples) and 105 (2 samples: suction and Winkler), 24 April 2005, K. Edward and S. Callan, WAMT71111-4; Eil Eil Spring, WA, 19°47'S, 121°26'E, 20 September 2002, K. Edward, in litter, WAM T71082; Hann Tableland, Qld, 16°49'S, 145°11'E, 950 m, 12 December 1995, G. Monteith, pyrethrum spray on bark, open forest, QM S38765; islands in Capricornia Cays National Park, Qld, pitfall trapping by QM and Queensland Parks and Wildlife Service: Masthead Island site 1, 23°32'24"S, 151°43'44"E, 0-5 m, 5-7 October 2008, grassed areas on beach, QM S17167; Erskine Island site 2, 23°30'07"S, 151°46'23"E, 2 m, 6-8 October 2008, open grassland, QM S17561; Lady Elliot Island site 7, 24°06'50"S, 152°42'58"E, 0-5 m, 29-31 March 2008, beach bean vine thicket, QM S16031; West Hoskyn Island site 1, 23°48'32"S, 152°17'20"E, 0-5 m, 13-15 May 2008, Casuarina stand, QM S17052; One Tree Island site 1, 23°30'25"S, 152°05'31"E, 0-5 m, 23-25 September 2008, Casuarina stand, QM S17144; North West Island site 8, 23°17'31"S, 151°42'29"E, 0-5 m, 9-11 October 2008, Casuarina stand, QM S17609; and Eungella, 21°12'S, 148°26'E, 600 m, 18 November 1981, Gillison, ANIC berlesate 984.


This species can be distinguished from other species in the genus by the presence of 3 or more transverse rows of barbate trichomes on collum and tergites 2 and 3, with 2 or more rows in remaining tergites, 3 basiconic sensilla on antennal article VI, long lateral palps on gnathochilarium (2.5 X diameter of medial palp). 2 setae on femur and 1 seta on tibia, funicle of setae of coxa, prefemur and femur ridged, ridges extending as projections surrounding flagellum, telotarsus with 2 processes (anterior and posterior) on claw, anterior spinous projection longer than claw, 3 ornamental trichomes c each side, caudal hooked trichomes with 1-4 hooks, absence of double pointed barbs on stem.


The original description by Verhoeff (1924) was very brief and no illustrations were given. A redescription of this species by Nguyen Duy-Jacquemin and Condé (1967) was based on a single paratype adult female preserved in ethanol from the Museum of Comparative Zoology, Harvard University. This description is detailed and clearly illustrated, but in light of recent collection of the species from eastern Australia and examination of large numbers of the museum specimens from a range of locations in Western Australia and Queensland, the species distribution can now be extended and variation in some characters recorded.

Additional description.

No freshly collected specimens available. All specimens had been preserved in 70% ethanol for at least 18 months prior to examination, with most in ethanol for decades. Body yellow brown in colour with trichomes including caudal bundle pigmented dark brown. Average length adult (mm): Barrow Island 2.1-2.5 (n = 3), Hann Tableland 3.0-3.4 (n = 5), Capricornia Cays 2.0-2.8 (n = 15); caudal bundle 0.4-0.5 mm. No differences observed between sexes. Variation in both pattern and number of trichomes on posterior vertex of head in specimens from different populations and variation within a population between specimens, and between left and right on a single individual. Pattern of 3 oblique rows each side separated medially by broad gap as described for paratype by Nguyen Duy-Jacquemin and Condé (1967) most common, but occasionally 2 rows, and 1 specimen with 5 rows each side. Trichomes barbate and longer than those of Unixenus attemsi . Variation in trichome number each side as follows: Barrow Island females 22-26 (n = 2), males 20-22 (n = 2); Eil Eil Spring subadult male 18-19; Eungella subadult male 19-21; Hann Tableland subadult males 19-25 (less in posterior row) (n = 3), adult females 23-32 (n = 5); Capricornia Cays, both males and females 17-23 (n = 12), plus 1 male with 5 rows, 34 each side. Clypeo-labrum as described for paratype by Nguyen Duy-Jacquemin and Condé (1967) for all specimens examined, with 12 setae along posterior margin, except for those from Queensland mainland sites Hann Tableland and Eungella with 10 setae (n = 11); further variation was also noted with a few specimens having 3 rather than 2 lamellar teeth each side along anterior margin. Occasional variation noted in number of sensilla on gnathochilarium with 20-22 sensilla each medial round palp and 12-13 each lateral palp. The majority have 22 sensilla on medial palp in contrast to the 21 in the single specimen described by Nguyen Duy-Jacquemin and Condé (1967).

Collum similar to description in Nguyen Duy-Jacquemin and Condé (1967) with trichomes in broad lateral clusters each side of wide medial gap equal to width of cluster, a posterior row extending from lateral edge of each cluster towards the midline. Barrow Island adult specimens similar to paratype ( Nguyen Duy-Jacquemin and Condé 1967) with continuous posterior row of trichomes and trichome insertion at midline. However in all other specimens examined, a median gap was present in the posterior row (Figs 3A and B). Number of trichomes each side median gap varied: Barrow Island 39-49 (n = 3), Eil Eil Spring 32-34 (n = 1, subadult male), Eungella 30-31 (n = 1, subadult male), Hann Tablelands 37-43 (n = 4), Capricornia Cays 35-57 (n = 12). In remaining tergites, only Barrow Island specimens were similar to the description by Nguyen Duy-Jacquemin and Condé (1967) with a continuous posterior row in all but tergite 10. In all other specimens examined, a median gap was present in the posterior row of most if not all tergites. Number of trichomes each side on tergite 2 variable: Barrow Island 46-60 (n = 3); Eil Eil Spring 39 (n = 1, subadult male); Eungella 36 (n = 1, subadult male); Hann Tablelands 48-66 (n = 4); Capricornia Cays 43-70 (n = 12). Tergal trichomes barbate and twice as long as those of Unixenus attemsi , trichomes longer in more posterior tergites. Males with coxal glands present on leg pairs 8 and 9.

Variation observed in number of ornamental trichomes a as follows (number given per side): Barrow Island 4-6 (n = 4, no differences between sexes); Eil Eil Spring 6 (n = 1, subadult male); Hann Tablelands: adult females 3-8 (n = 5), subadult males 8 -12 (n = 3); Eungella 7-8 (n = 1, subadult male); Capricornia Cays 4-9 (n = 13, no differences between sexes). Hooked caudal trichomes with 1-4 hooks on barbed stems, barbs all distal-facing (Fig. 3E).


Unixenus mjoebergi has been identified in north western and north eastern Australia, including islands off the coast on either side of the continent (Fig. 8). The lack of records for central Australia and Northern Territory is possibly more a reflection of very limited and untargeted collecting effort rather than actual absence of the species from these regions. The species is found in litter of treed habitats (both open and closed forest types), and occasionally in sandy beach and sand dune habitats.


The specimens examined showed variation in a number of characters, with those of the single female adult paratype described by Nguyen Duy-Jacquemin and Condé (1967) falling within the range for each. Of particular interest is the variation in pattern of tergal trichomes with only the Barrow Island specimens showing the same pattern as the paratype. All specimens from Queensland, as well as the single specimen from Eil Eil Spring, showed a distinct gap in all or almost all tergites (the only exception were two specimens that lacked a gap in posterior row of tergites 4 and 5). Numbers of trichomes, including the ornamental trichomes a, varied also with no distinct geographic pattern discernible. The wide distribution, and presence of the species on islands on both sides of the continent points to the possible movement of the species by birds and or wind.

In the course of this study, collections from the Hamersley Ranges of Western Australia previously identified as Unixenus mjoebergi were found to have a number of important differences requiring erection of a new species, Unixenus karajinensis sp. n.