A new, alpine species of Lissodesmus Chamberlin, 1920 from Tasmania, Australia (Diplopoda, Polydesmida, Dalodesmidae)

Abstract Lissodesmus nivalis sp. n. is described from 1450–1550 m elevation on the treeless, alpine Ben Lomond plateau in northeast Tasmania, Australia. The new species is distinguished from all other Tasmanian and Victorian Lissodesmus species by a unique combination of gonopod telopodite features: solenomere without a pre-apical process, tibiotarsus Y-shaped, femoral process L-shaped with forked tips, prefemoral process with a long comb of teeth below an irregularly dentate apical margin, and a roughened “shoulder process” near the base of the prefemoral process.


Introduction
Several species of the millipede family Dalodesmidae can be found in treeless alpine areas of Tasmania, among them Dasystigma margaretae (Jeekel, 1984), which was collected on an alpine "cushion plant" at 1150 m at the type locality on Tasmania's Central Plateau (Mesibov 2003). However, until recently the only Tasmanian dalodesmid known exclusively from above the treeline was Noteremus summus Mesibov, 2009 from the summit of Mt Weld (1100-1300 m) in the south of the island (Mesibov 2009). The new species described here is so far known only from ca 1450-1550 m on the Ben Lomond  , 1934-2018 (black squares), major roads (thin red lines) and 1300 m elevation contours (thick blue lines); the large, rectangular block above 1300 m is the Ben Lomond plateau B Aerial photograph of part of the Ben Lomond plateau with Lissodesmus nivalis sp. n. localities: 1 = Ben Lomond ski village (type locality), 2 = Surprise Vale, 3 = Giblin Fells C Ben Lomond ski village collecting site (1 in B), 2 April 2018; white arrow indicates the rock-hugging shrub beneath which the holotype and paratypes of L. nivalis sp. n. were found. Sampling sites in A from Mesibov (2006Mesibov ( -2018 for named species, and the author's unpublished records for undescribed species. Image in B from https://maps.thelist.tas.gov.au/listmap/app/list/map. Rectangle in inset map in C shows extent of map A both maps are Mercator projections. plateau in northeast Tasmania (Fig. 1). Its discovery in 2017 was remarkable for another reason: northeast Tasmania has been intensively sampled for millipedes by the author and other collectors over many years (Fig. 1A). I therefore thought the list of the region's dalodesmid fauna might be complete, apart from very small, inconspicuous and geographically restricted forms yet to be collected. Unexpectedly, the new Ben Lomond species is a large and conspicuous addition to the Tasmanian and Victorian genus Lissodesmus Chamberlin, 1920, which now includes 30 species (Mesibov 2006(Mesibov -2018.

Materials and methods
All specimens are stored in 80% ethanol in the Queen Victoria Museum and Art Gallery (QVM). Several legs of the holotype were removed and placed in 95% ethanol before the rest of the specimen was preserved. Freshly collected specimens were examined and measured using a Nikon SMZ800 binocular dissecting microscope, and stacks of colour images were manually generated using a Canon EOS 1000D digital SLR camera mounted on the Nikon SMZ800 fitted with a beam splitter. Images were then focus-stacked with Zerene Stacker 1.04 software. The gonopods and one leg 7 of the male paratype were cleared in 80% lactic acid and temporarily mounted in a 1:1 glycerol:water mixture for examination. The gonopods were imaged using an eyepiece video camera mounted on an Amscope binocular microscope. Preliminary drawings were traced from printed copies of the images, then corrected by reference to the actual gonopod. Figures were composed using GIMP 2.8 and maps with QGIS 2.14.
Locality details are given with latitude and longitude in decimal degrees based on the WGS84 datum. The estimated uncertainty for a locality is the radius of a circle around the given position in metres.
Gonopore small, opening on rounded, mediodistal enlargement of leg 2 coxa. Gonopod telopodites extending to leg 5 bases when retracted; bases of legs 6 and 7 well-separated, coxae of legs 6 and 7 slightly swollen ventrally; sternite between legs 6 and 7 slightly excavate, with brushes of long, stiff setae on sternite just medial to coxae. Aperture ovoid but with anterior margin straight, wider than long, about 1/2 the width of ring 7 prozonite, rim slightly raised laterally.
Gonopods: gonocoxae truncate-conical, tapering distally, lightly joined medially, moderately setose on posterobasal surface. Telopodite (Figs 2C, 3) long, slender, gently curving anteriorly from base, with a band of long setae (Fig. 3C) on posterolateral surface from telopodite base almost to level of solenomere base. Telopodite base tapering from thickened basal rim. Cannula prominent, entering telopodite base in excavation lined with fine setae; prostatic groove running on anterior surface of telopodite before joining base of solenomere, opening at solenomere tip. Solenomere thin, rod-like, tapering to point, arising at ca 1/2 telopodite height on anteromedial surface, directed a little posterodistally before curving anterodistally. Tibiotarsus arising on posterior surface a little distal to level of solenomere base, thicker than solenomere, directed distomedially, apex bifurcated, the tips blunt. Femoral process arising on anterolateral surface distal to tibiotarsus origin, L-shaped; the longer portion of the "L" directed posterodistally with a forked tip; the shorter portion of the "L" directed posterobasally, also with forked tip but with distal portion of fork larger than basal portion. In distal 1/3 of telopodite, prefemoral process separated on posteromedial side from prominent, tab-like "shoulder" process with irregularly and bluntly toothed margin. Prefemoral process flattened anterolaterally, curving medially near obliquely truncate apex, with apical margin irregularly and bluntly toothed and with ca 15 discrete teeth forming comb on posterior margin.
Female closely resembling male but a little wider; legs not swollen. Genital aperture with posterior margin rounded-triangular medially; cyphopods not examined.
Name. Latin nivalis, of snow; adjective. This species spends several months each winter with its habitat covered in snow.
Distribution. So far known only from alpine moorland and shrubland at three localities on the Ben Lomond plateau in northeast Tasmania (Fig. 1A, B). Found in peaty material under prostrate and rock-hugging alpine shrubs (Fig. 1C).
Remarks. The gonopod telopodite of L. nivalis sp. n. shares several features with other Tasmanian Lissodesmus species. As in L. anas and L. horridomontis, for example, the prefemoral process is offset laterally by the distal development of a roughened, tablike "shoulder" process. The tibiotarsus has a bifurcated tip, as in L. cornutus and L. montanus, and the femoral process is L-shaped, as in L. clivulus and L. latus. However, the distinctive combination of telopodite characters in L. nivalis sp. n. makes it hard to judge from morphology what its nearest relation in the genus might be. It is quite unlike the five other Lissodesmus species found in the Ben Lomond area, namely L. adrianae, L. cognatus, L. devexus, L. hamatus and L. plomleyi.
The upright portion of the femoral process "L" is doubly forked on the left gonopod of the paratype male (Fig. 3D). There is no second bifurcation on the right gonopod of the paratype, or on the femoral processes of the holotype, so the double forking appears to be a developmental abnormality. (The third, non-type male is missing its femoral processes.) The holotype and paratypes were collected by Tasmanian land snail specialist Kevin Bonham in company with the author. We searched the group of rocks shown in Fig. 1C and similar nearby habitats for more than an hour but found no more L. nivalis sp. n., although we saw scattered specimens of the common northeast Tasmanian dalodesmids L. adrianae and Tasmaniosoma clarksonorum Mesibov, 2010. My collecting in November 2017 was even less successful, yielding only one presumed juvenile of L. nivalis sp. n., despite my searching a larger area of apparently suitable shrub habitat for several hours. L. nivalis sp. n. may be naturally scarce in its alpine habitat.
The types were collected live and transported from the field in a collecting jar filled with peaty material. As often happens when dalodesmids are live-collected, the female and one of the males (the holotype) mated in the jar and were still in copula when killed by freezing several hours later. In Fig. 2C, white amorphous material (spermatic fluid?) can be seen adhering to the gonopod telopodites of the holotype.