The genus Unixenus Jones, 1944 (Diplopoda, Penicillata, Polyxenida) in Australia

Abstract The penicillate genus Unixenus Jones, 1944 is widespread, with species found in Africa, Madagascar, India and Australia. Each of the two Australian species was originally described from single samples from Western Australia. In this study, collections of Penicillata from museums in all states of Australia were examined to provide further details of the two described species, to revise the diagnoses for both the genus and the species, and to better understand the distribution of the two species in Australia. In addition, two new species Unixenus karajinensis sp. n. and Unixenus corticolus sp. n. are described.


Introduction
created the genus Monoxenus for his type species Monoxenus padmanabhii collected from the Trivandrum region in Southern India, later renaming it Unixenus Jones, 1944, because Monoxenus had been preoccupied by a genus in Cerambycidae (Coleoptera). Jones distinguished Unixenus from the genus Monographis Attems, 1907 on the grounds that the new genus had shorter tergal setae and caudal trichomes with one to five hooks rather than two hooks. However, these characters can vary within a genus, for example Propolyxenus Silvestri, 1948 (Short andHuynh 2010). Silvestri (1948) separated Monographis from Unixenus on the basis of the absence of the tarsal spine and this absence was then used (Nguyen Duy-Jacquemin and Condé 1967) to create the two Australian species Unixenus attemsi Nguyen Duy-Jacquemin and Condé, 1967, based on specimens originally identified by Attems (1911) as the African Monographis schultzei Attems, 1909, and Unixenus mjoebergi (Verhoeff, 1924) originally placed in Monographis. Nguyen Duy-Jacquemin and Condé (1967) also reassigned two species formerly placed in the genus Saroxenus Cook, 1896 to the genus Unixenus, namely Saroxenus broelemanni Condé & Jacquemin, 1962 from Madagascar and Saroxenus vuillaumei Condé & Terver, 1963 from the Ivory Coast. In this paper, additional characteristics of the two species Unixenus mjoebergi and U. attemsi are described based on examination of numerous museum specimens and fresh material collected by the authors. Two new species from Australia are also described.

Materials and methods
Some specimens for this study were obtained by sieving samples of bark and decomposing leaf litter into a white tray and hand-picking into 70% ethanol. The majority of specimens in this study, however, came from Australian museum collections. Specimens were examined using light and scanning electron microscopy. For light microscopy, specimens were cleared in 15% potassium hydroxide, heated in a water-bath for 2 minutes at 80°C, neutralised in 20% acetic acid for 2 minutes, rinsed in distilled water and dehydrated in a series of ethanol baths prior to staining with 1% Fast Green solution to increase contrast. The head and body were separated, the body cut open with a single latero-longitudinal incision and contents removed. After rinsing in 100% ethanol, stained specimens were transferred to 100% isopropanol, then to xylene and mounted on slides with DPX synthetic resin. Scanning electron micrographs were obtained for adults of U. corticolus sp. n., and adults and one subadult stadium VII of U. karajinensis sp. n. The specimens were preserved in 70% ethanol prior to being gently mounted on stubs using adhesive tabs, then air-dried, sputter-coated with gold and examined with a Philips XL20 scanning electron microscope.
Specimen lengths were measured from head to telson with caudal bundle of trichomes excluded. Adults were sexed when possible. Measurements are an indication only of size as length varies with state of activity in life and state of preservation in death. Naming of the leg segments follows Manton (1956). Unless otherwise indicated, all millipedes referred to are adults (stadium VIII). Stadium VII specimens are referred to as subadult, and "immature" refers to any non-adult stadium. The trichomes in a transverse row on the telson dorsal to the caudal bundle are referred to as ornamental trichomes.
Abbreviations Diagnosis. This species can be distinguished from other species in the genus by the presence of 2 transverse rows only of short barbate trichomes on collum and tergites, 3 basiconic sensilla on antennal article VI, long lateral palps on gnathochilarium (2.5 X diameter of medial palp), 1 seta on femur and no setae on tibia, funicle of leg setae with no projecting spines, telotarsus with 4-6 processes on claw, thin anterior spinous projection same length as claw, 3 ornamental trichomes c each side, caudal hooked trichomes with 3-11 hooks with double pointed barbs on stem of trichomes with 4 or more hooks.
Remarks. The original description by Attems (1911) was very brief. A redescription of the species by Nguyen Duy-Jacquemin and Condé (1967) was based on examination of two female specimens from Torbay in southern Western Australia (the type locality) held in the Zoology Museum, Hamburg, Germany (coll. by Hamburg S.W. Australia Expedition 1905). 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 species from a range of locations in WA, the species description can now be expanded and variation in some characters recorded.
Single caudal bundle of hooked trichomes, 2-11 hooks with barbed stems, size of hook and nature of barbed stem dependent on number of hooks: trichomes with 2-4 hooks, hooks large, all barbs on stem distal-facing similar to those in U. mjoebergi ( Fig. 3E), trichomes with 4-11 hooks, hooks smaller and with double barbs along stem proximally, with both proximal-and distal-facing points (Fig. 3D). Specimens examined by Nguyen Duy-Jacquemin and Condé (1967) had 5-7 hooks, with no description given of barbs along stem.
Distribution. This species is widespread in Australia ( Fig. 8) but appears to be most common in a range of habitats in southern WA. The most northerly collection is Bush Bay, WA, 25°07'03"S, 113°48'22"E, where it was collected together with U. mjoebergi (WAM T71125). In eastern Australia the species appears to be restricted to dry woodlands. It is found under bark of Eucalyptus in small aggregations, often with many exuviae, as well as in dry leaf litter and under stones in treed areas on welldrained sandy or sandy loam soil.
Remarks. The two Torbay specimens described by Nguyen Duy-Jacquemin and Condé (1967) are longer than almost all measured in this study, at 2.25 and 2.65 mm. Torbay is on the south coast of WA (Fig. 8) and a single specimen in the WAM collection (T71144) from Walpole-Nornalup National Park on the south coast of WA is also large (2.3 mm). All adults from eastern Australia are smaller. Smaller adults have fewer trichomes on head and vertex.  (Verhoeff, 1924) http://species-id.net/wiki/Unixenus_mjoebergi Figs 1B, 3A, 3B, 3E
Remarks. 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 U. 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).
Distribution. 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.
Remarks. 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. Diagnosis. Differs from Unixenus mjoebergi in longer and thinner tergal trichomes, 6 pairs of coxal glands in males on leg pairs 6-11, telotarsus with anterior spinous projection shorter than claw, 8 ornamental trichomes c each side. Antennal articles VI and VII with distinctive notched appearance at distal edge, arrangement of sensilla in article VI with setiform sensillum anterior to 3 basiconic sensilla. Number of setae on coxae 3-13 varies more widely from 1-6 in contrast to 2-3 in U. mjoebergi. The hooked caudal trichomes have double barbs proximal to the hooks, last sternal plate with 2 setae.

Unixenus karajinensis
Etymology. The Australian aboriginal Banyjima people's name for the Hamersley Ranges is Karajini.
Description. Length of both sexes 2.8-3.3 mm, caudal bundle 0.3 mm. Colouration in alcohol both sexes yellow brown with trichomes including caudal bundle medium to dark brown, long ornamental trichomes darker.
Antennae with proportions of 8 articles and 4 sensory cones typical of other species in genus (Figs 4B and 5B). Antennal articles VI and VII with distinctive notched appearance at distal edge (Fig. 5A), article VI with 3 thick basiconic sensilla of equal length, coeloconic sensillum posterior to basiconic sensilla, setiform sensillum anterior to basiconic sensilla. Antennal segment VII typical of genus with 1 coeloconic sensillum to the posterior followed anteriorly by 2 thick basiconic sensilla of similar height; 1 setiform sensillum between the basiconic sensilla (Fig. 4C). Clypeo-labrum with 12 setae along posterior margin, anterior margin with no dentition lateral to median cleft, two thirds surface covered with spherical papillae, papillae reducing in size to the posterior margin and lacking hairs (Fig 4D). Gnathochilarium with length lateral palp at least 2 X diameter medial palp; lateral palp with 13 cylindrical sensilla, medial palp 21 sensilla (Figs 4E and 5E).
Collum with almost symmetrical arrangement of trichomes, posterior row of trichomes with broad medial gap, extending to lateral clusters of trichomes, anteriorly a narrowing band of trichomes extending from each lateral cluster towards midline, scattered trichomes between posterior row and anterior bands (Fig. 4F). Number of trichomes 56L + 59R in holotype male; variation common with range per side: Wittenoom female paratypes 31-46 (n = 6); Tom Price paratype females 33-47 (n = 4), paratype males 37-43 (n = 3). Small lateral protuberances each with row of 6 forward-facing trichomes in holotype, varying between 4-6 in Tom Price and Wittenoom paratypes.
Telson with ornamental trichomes arranged almost symmetrically with 5 trichomes (some variants with 4-8) a, 1b, and 8c each side of midline (Fig. 4J). Insertion points vary in size with a and c bigger than b. Single caudal bundle of hooked trichomes with 2-4 hooks and barbed stems. Double barbs of stem showing both distal-and proximal-facing barbs (Fig. 4K). Double barbs start immediately below hooks on 4 hook trichomes, with simple distal-facing barbs before first double barb on 2-3 hook trichomes. In immature stadia, two clusters of short barbate trichomes with same structure as ornamental trichomes a found ventral to caudal bundle (Fig. 5D). These clusters also observed in other species in the family Polyxenidae. They displace laterally after moulting to become pleural projections.
Distribution. This species is only known from three sites in the Hamersley Ranges, WA (Fig. 8). Both males and females were collected at each location. Since collection, the asbestos mine at Wittenoom has been closed and access restricted to the area that includes the type locality.
Remarks. The widespread distributions of U. attemsi, U. mjoebergi and U. corticolus sp. n. are not unexpected as their small size, bristles and very light weight make it probable that they are blown by the wind or become attached to bird feathers. Unexpectedly U. karajinensis sp. n. appears to be limited to a single mountain range, although further sampling may extend the distribution. Paratypes. One male, five females, same data as holotype, mounted on slides, male: MV K-11508, females 1-5: MV K-11509-13; one male and one female from Tidal River, Wilson's Promontory, Vic, 39°01'54"S, 146°18'49"E, 1 November 2005, C. Huynh, in Melaleuca bark, mounted on slides, male: MV K-11514, female: MV K-11515.
Diagnosis. 4 basiconic sensilla on antennal article VI, basiconic sensillum 4 posterior to coeloconic sensillum, short lateral palps on gnathochilarium (1.5 X diameter of medial palp), 1 seta on femur and no setae on tibia, 5 ornamental trichomes c each side, caudal hooked trichomes with 3-6 hooks. Setae of coxa, prefemur and femur similar to that of U. mjoebergi but with slightly curving and fewer ridges on funicle.
Description. Length of both sexes 2.4-3.4 mm, caudal bundle 0.45 mm. Colour dark grey with broad unpigmented band dorsally along midline. Trichomes unpigmented, appearing translucent white in live specimen, long ornamental trichomes c darkly pigmented in contrast to trichomes of caudal bundle that appear white in live specimens.
Head (Fig. 6A) with 8 ocelli each side: 4 dorsal, 4 lateral (1 anterior, 2 medial and 1 posterior). Vertex with 2 posterior groups of trichomes arranged in 2 oblique rows, separated medially by a broad space. Number of trichomes varies, holotype with 10L+10R (anterior rows) and 7L+6R (posterior rows), total each side 17L and 16R. Number of trichomes per side varies 14-18, with no differences between sexes, asymmetrical pattern common with maximum difference 2 trichomes. Trichobothria equal in size, arranged in triangle with angle at b >120 o , distance a-b slightly shorter than distance b-c.
Collum with almost symmetrical arrangement of trichomes, 2 main rows of trichomes each side of medial gap with small number of trichomes between rows, rows linked laterally with small cluster of trichomes (Fig. 6F). Trichomes 24L+23R in holotype, varying between 23-28 per side in paratypes. Small lateral protuberances each with row of 5 forward facing trichomes in holotype, 3-7 in paratypes. In tergites 2-10, trichomes arranged on posterior half of tergite in 2 loose rows with small clusters laterally (Fig. 6F). Trichomes in anterior row directed towards head, those of posterior row directed posteriorly. Trichome number on tergite 2 variable: 26L+26R in holotype, 24-34 each side in paratypes. Conical pleural projections along each side associated with tergites 2-10. Tergal trichomes, all short, barbate and thicker than those of U. mjoebergi and U. karajinensis with three internal longitudinal rows of projections (Figs 6M and 7C), pleural trichomes slightly longer.
Distribution. Specimens of this species have been found at a number of locations some distance from each other in southern Australia (Fig. 8). Specimens were collected from under bark of Eucalyptus, Melaleuca and Leptospermum. The species was found once only on the ground, in litter formed from mulched bark. Males and females were collected at each location. No specimens were found in museum collections.
Remarks. Although this species is similar in many ways to U. mjoebergi, it appears to have different habitat requirements as it is rarely found in litter, and then only in bark mulch. This would explain the absence of the species from museum collections that are mainly the result of pitfall trapping or extraction from litter.

Key to described species of Unixenus
The type species from India, U. padmanabhii, is not included as insufficient details are known: 1a. Presence