Four new species of Unixenus Jones, 1944 (Diplopoda, Penicillata, Polyxenida) from Australia

Abstract Unixenus carnarvonensis sp. n., Unixenus corringlensis sp. n., Unixenus barrabaensis sp. n. and Unixenus myallensis sp. n. are described from Australia. A revised diagnosis of Unixenus karajinensis and new details on the distribution of the species are given. A key is presented to 10 of all 11 currently known species of the genus.


Introduction
Unixenus Jones, 1944 is a widespread genus in the family Polyxenidae in the single order Polyxenida within the millipede subclass Penicillata. The genus is characterised by the presence of a single generalised type I caudal bundle of trichomes (Condé and Nguyen Duy-Jacquemin 2008) with a linear arrangement of ornamental trichomes above, and antennal articles VII with 2 thick basiconic sensilla, 1 setiform sensillum between, and 1 coeloconic sensillum posteriorly. Barbate trichomes are arranged posteriorly on each tergite in 2 or more rows with trichomes arranged in 2 broad clusters laterally. Tarsus 2 has one small seta.
Seven species have been described in Unixenus. The type species Unixenus padmanabhii (Jones, 1937) from India, U. broelemanni (Condé & Jacquemin, 1962) from Madagascar, U. vuillaumei (Condé & Terver, 1963) from Ivory Coast and four Australian species U. mjoebergi (Verhoeff, 1924), U. attemsi Nguyen Duy-Jacquemin & Condé, 1967, U. karajinenis Short & Huynh, 2011 and U. corticolus Short & Huynh, 2011. In this paper, four new species of Unixenus from Australia are described. A revised diagnosis together with an expanded distribution is given for the recently described species U. karajinensis, previously identified from just three locations in the Hamersley Ranges in the Pilbara, WA.

Methods
The specimens in this study came from the collections of the Australian Museum in Sydney, NSW and the Western Australian museum, Perth, WA. Specimens were examined using light 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.
Specimen lengths were measured from head to telson with the caudal bundle of trichomes excluded. Adults were sexed when possible. 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: AM = Australian Museum, Sydney, New South Wales; NSW = New South Wales; WA = Western Australia; WAM = Western Australian Museum, Perth; L = left; R = right.
rior rows merging laterally to form rosettes of trichomes, and further trichomes scattered between these rows. Small lateral protuberances each with row of 4-6 forward facing trichomes (Fig. 1E). Tergites 2-9 with trichomes arranged on posterior half of the tergite with one distinct posterior row with a medial gap and ending with small clusters later- ally. Further trichomes anterior to this row loosely arranged in two to three rows (Fig.  1E). Anterior trichomes directed towards head while remaining trichomes directed posteriorly. Tergite 10 with 2 rows of trichomes arranged along posterior edge with broad medial gap (Fig. 1E). Conical pleural projections along each side associated with tergites 2-10, each with a dense cluster of trichomes. Tergal trichomes barbate, same structure as U. mjoebergi.
Telson with ornamental trichome insertions arranged almost symmetrically with 6-10 trichomes a, 1b, and 3c each side of the midline (holotype has 4 trichomes c on right side). Large insertion points for trichomes b (Fig. 1J). A small indentation external to trichomes c, either side. Single caudal bundle typical of genus. Hooked caudal trichomes with 2-5 hooks on barbed stems, majority with distal facing barbs only along stem proximal to hooks (Fig. 1K), some with distal and proximal facing barbs.
Distribution. So far known only from two sites in the Carnarvon region of Western Australia (Fig. 5). Co-occurs with U. mjoebergi.
Remarks. This species is very similar to U. mjoebergi and cannot be separated without examination under high magnification.  on femur and 1 seta on tibia, maximum of 3 setae on coxa, broad gap between anterior rows of trichomes on vertex and posterior rows, and in arrangement of posterior rows.

Unixenus corringlensis
Description. As for U. carnarvonensis sp. n., differing in the following details: Measurements: Body length 2.3-2.5 mm with no differences between sexes, caudal bundle 0.3 mm.
No freshly collected specimens available. Specimens had been preserved in 70% ethanol. Body yellow brown in colour with tergal trichomes medium brown.
Telson with ornamental trichome insertions numbering 7-10a, 1b, and 3c each side of the midline (Fig. 2I). Trichome b insertion points small, typical of the genus. Hooked caudal trichomes with 2-4 hooks on barbed stems, distal facing barbs along stem proximal to hooks, most distal barb larger. Caudal trichomes with 2 hooks only in both holotype and paratype from Corringle State Forest (Fig. 2H).
Distribution. So far known only from State forest at two widely separated sites in mid NSW and one site in northern NSW (Fig. 5).  No freshly collected specimens available. Specimens had been preserved in 70% ethanol. Body yellow brown in colour with brown tergal trichomes.
Telson with ornamental trichome insertions numbering 6-8a, 1b, and 3c each side of the midline, arrangement typical for the genus, as illustrated for U. corringlensis. These trichomes barbate, long and straight. Hooked caudal trichomes with 1-3 hooks on barbed stems, majority with distal facing barbs only along stem proximal to hooks, very small number with distal and proximal facing barbs.
Distribution. So far known only from three forested sites in northern NSW, with a north-south range of ca 200 km (Fig. 5).  Etymology. For Myall Lakes National Park, the type locality; adjective. Diagnosis. Similar chaetotaxy to U. attemsi with 1 seta on femur and none on tibia, setae smooth biarticulate; differs from U. attemsi in having a gap between anterior and posterior vertex groups of trichomes, 4 basiconic sensilla on antennal article VI, gnathochilarium with short lateral palps (1.5 × diameter of medial palp) bearing 12-13 short rounded sensilla, ornamental trichome insertions c in row.
Colouration: No freshly collected specimens available. Specimens had been preserved in 70% ethanol. Body yellow brown in colour with black trichomes including caudal bundle dark brown -black.
Collum with two rows of trichomes sparsely arranged each side of a medial gap, rows merge laterally to form rosettes of trichomes, and with a small number (2 each side in holotype) of trichomes between the two rows. Lateral protuberances of collum with 3-4 trichomes each. Tergites 2-10 with trichomes arranged most commonly in 2 rows on posterior half of the tergite each side of a medial gap. Anterior row sinuous with small gap to lateral cluster. In posterior tergites the two rows are closer together and straighter (Fig. 4F). In some specimens tergites 2 and 3 have scattered trichomes between the anterior and posterior rows forming an intermediate 3 rd row. Conical pleural projections along each side associated with tergites 2-10, each with dense cluster of short dark trichomes. Tergal trichomes of posterior tergites longer than those of anterior tergites.
Telson with ornamental trichome insertions numbering 5-6a, 1b and 3c each side of the midline, with c trichome insertions in straight line (Fig. 4K). Trichomes b and c black in colour. Hooked caudal trichomes with 1-6 hooks on barbed stems, majority with distal facing barbs only along stem proximal to hooks, with occasional double barbs with both distal and proximal facing projections (Fig. 4L).
Distribution. So far known only from two treed coastal sites in mid NSW, with a north-south range of ca 150 km (Fig. 5).  Revised diagnosis. Differs from U. 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 the claw, 5-9 ornamental trichomes c each side. Antennal articles VI and VII with distinctive notched appearance at the distal edge, 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. The last sternal plate has 2 setae.

Unixenus karajinensis
Remarks. Examination of further specimens of U. karajinenis has confirmed that the original diagnosis for the species is in error in stating that the number of ornamental trichomes c is 8 each side (Short and Huynh 2011). Although the number is 8 each side in the majority of specimens examined, the number can vary from 5-9.
A number of the collections examined were from the two previous collection sites: the type locality Wittenoom and the nearby township of Tom Price. However the species has now been identified from two further locations in the Pilbara region of Western Australia, with one site being 200 km from the type locality indicating that its distribution is not as tightly restricted to the Hamersley Ranges as originally recorded (Fig. 5).
Collections were sent to WAM for identification after reports from 1972 of the millipedes reaching nuisance proportions in parts of the Pilbara, particularly the Hamersley Ranges area and the townships of Tom Price and Wittenoom (Koch 1985). Koch identified the species involved as U. mjoebergi and a study was done for the Western Australian Department of Agriculture (Burt 1984) to determine ways of reducing millipede numbers and swarming behaviour. However after recent examination of collections in WAM it appears that U. karajinensis also occurred in huge numbers and has been found associated with housing. It appears very likely to have been involved in swarming behaviour.

Discussion
The genus Unixenus is widespread and speciose. It is likely further species will be identified. The genus is not limited to Australia. Apart from U. padmanabhii in India, U. vuillaumei in Ivory Coast and U. broelemanni in Madagascar, specimens from two locations in Vietnam have been identified as Unixenus by Nguyen Duy-Jacquemin and Condé (1967), as well as two specimens from Vietnam retrieved from imported tropical fruit by the Australian Quarantine and Inspection Service and identified by the authors (QM collection QMS 25102, prepared as slides) as being in the genus Unixenus. Specimens from 3 locations in Papua New Guinea have been identified as 3 distinct species of Unixenus (Nguyen Duy-Jacquemin and Condé 1982, Condé andNguyen Duy-Jacquemin 1984). The specimens are tiny juveniles (stadia II and III) and were identified as Unixenus, most probably from 3 undescribed species. Adult or subadult specimens will be required for complete identification.

Updated Key to described species of Unixenus
The type species from India, U. padmanabhii is not included as insufficient details are known.
Unfortunately the species in the genus Unixenus are very similar and reliable characters suitable for identification are only visible under high magnification, requiring preparation of slides. The key should be used with some caution as although it has been developed using characters that are consistent in the individuals examined for each species, there may be some variability in characters that has not been discernable due to the limited number of adult individuals available for examination.