Research Article |
Corresponding author: Robert Mesibov ( robert.mesibov@gmail.com ) Academic editor: Pavel Stoev
© 2014 Robert Mesibov.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Mesibov R (2014) The Australian millipede Dicranogonus pix Jeekel, 1982 (Diplopoda, Polydesmida, Paradoxosomatidae): a species with and without paranota. ZooKeys 454: 29-39. https://doi.org/10.3897/zookeys.454.8625
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Dicranogonus pix Jeekel, 1982 occurs in Victoria and Tasmania, Australia, including the islands in eastern Bass Strait between the two States. There is only slight gonopod variation across this range, but D. pix populations with and without paranota are separated in Bass Strait by the ca 50 km-wide gap between the Kent and Furneaux Groups of islands.
Millipede, Diplopoda , Polydesmida , Paradoxosomatidae , Tasmania, Victoria, Bass Strait, Australia, biogeography
Dicranogonus was erected by
Somewhat cryptically,
In 1984, Jeekel proposed that Victoria had been a centre of dispersal for Dicranogonus, Pogonosternum Jeekel, 1965 and Somethus Chamberlin, 1920 (
In a later publication, however, Jeekel mentioned that Dicranogonus also occurs in Tasmania (
As shown below, Dicranogonus occurs in two strikingly different forms: one in Victoria and northeast Bass Strait with obvious paranota, and one without paranota in southeast Bass Strait (in the Furneaux Group) and on the northeast Tasmanian mainland. In this paper I treat both forms as D. pix, and in the Discussion section I explain the reasons for this taxonomic decision.
All specimens I examined are in registered specimen lots in Australian repositories and are listed in the accompanying data table. Latitude/longitude figures in the table are given with the WGS84 datum together with my estimate of the spatial uncertainty (Darwin Core CoordinateUncertaintyInMeters).
Colour photomicrographs of specimens in 80% ethanol were taken with a Canon EOS 1000D digital SLR camera mounted on a Nikon SMZ800 binocular dissecting microscope equipped with a beam splitter. Colour images used in the figures are focus-stacked composites prepared with Zerene Stacker 1.04 software. Grayscale images of gonopod telopodites temporarily mounted in 1:1 glycerol:water were captured as screenshots from the output of a 1.3 megapixel digital video eyepiece camera mounted in one ocular tube of a Tasco LMSMB binocular microscope. The screenshots were edited with GIMP 2.8 software to remove background highlights and artefacts. Measurements were made in all cases to the nearest 0.1 mm with eyepiece grids and reference scales. The SEM images in Fig.
Abbreviations below and in the accompanying data table: AM = Australian Museum, Sydney, New South Wales, Australia; DPIPWE = New Town Laboratories, Department of Primary Industries, Parks, Water and Environment, New Town, Tasmania, Australia; NBC = Naturalis Biodiversity Center, Leiden, Netherlands; NMV = Museum Victoria, Melbourne, Victoria, Australia; NSW = New South Wales, Australia; QVM = Queen Victoria Museum and Art Gallery, Launceston, Tasmania, Australia; Tas = Tasmania, Australia; TMAG = Tasmanian Museum and Art Gallery, Hobart, Tas; Vic = Victoria, Australia.
Dicranogonus:
Dicranogonus pix Jeekel, 1982, by original designation.
Dicranogonus pix
Gonopods. The gonopod telopodite varies only slightly in details over the D. pix range (Figs
Dicranogonus pix Jeekel, 1982, right gonopod telopodite, anterior views. A Holotype, from Fig.
Dicranogonus pix Jeekel, 1982, known localities as of 17 September 2014. A Localities with males (squares) and with females only (triangles); labels indicate localities of males with gonopods imaged in Figs
Paranota. In agreement with the original description of D. pix, the diplosegments of a nearly topotypical male have obvious paranota (Figs
The only exceptions to this simple geographical pattern in the material examined are three males and two females lacking paranota from the Buchan district in eastern Victoria, collected in 1907 (Figs
Other characters. I add here only a few minor details to the very clearly written, 1600-word description by
D. pix and Notodesmus scotius Chamberlin, 1920 are the only Polydesmida so far known to occur naturally on both sides of Bass Strait (see N. scotius distribution records and KML file at http://www.polydesmida.info/millipedesofaustralia/localities.html). The N. scotius material I have examined is uniform throughout the species’ range in Tasmania, Victoria and southeast New South Wales, and I have not detected any morphological discontinuity in N. scotius in Bass Strait.
For other poorly vagile animals with trans-Bass Strait distributions, I have not yet found any documentation of discontinuities congruent with the paranota/no-paranota divide in D. pix between the Kent and Furneaux Groups. A possible evolutionary parallel is in the rhaphidophorid cricket genus Cavernotettix Richards, 1966. C. flindersensis (Chopard, 1944) is known only from the Furneaux Group, and C. craggiensis Richards, 1974 is known only from Craggy Island (ca 40 ha), located between the Kent and Furneaux Groups. (Cavernotettix records from the online Atlas of Living Australia, http://www.ala.org.au, accessed 17 September 2014.)
Within Victoria the known distribution of D. pix is a zone ca 150 km long and up to 60 km wide, running north from East Gippsland over the Great Dividing Range, from near sea level to ca 600 m. On the Tasmanian mainland all but one of the locality records are less than ca 2 km from the sea, the exception being a 1964 collection from Gladstone, a small town. “Gladstone”, however, may only represent the nearest named place to a coastal collecting site on Ringarooma Bay, ca 15 km distant. I have collected N. scotius, but not yet D. pix, in the dry eucalypt forests beginning ca 10 km inland from D. pix localities along the northeast Tasmanian coast.
Ecology.
Surprisingly, D. pix was missing from pitfall samples collected in coastal heathland within the D. pix range in northeast Tasmania in 1986-88. The sampling was carried out by T.B. Churchill, who trapped paradoxosomatids (as by-catch) in three 9 × 9 m pitfall arrays (nine evenly spaced traps per array) located at each of four 90 × 90 m sampling sites, with the traps emptied once a month for 14 months (
Holotype male: “Sta. 86. 4 km ESE Bruthen... Eucalyptus forest, State forest, under logs” [My location estimate for the type locality near Bruthen, Vic is 37°43'18"S 147°52'24"E ±1 km, probably along the Bruthen-Buchan Road.]
Paratypes: 3 males, 6 females, details as for holotype; 38 males, 29 females, “Sta. 85. 13 km SE Buchan... Eucalyptus forest, State forest, under logs” [37°36'S 148°11'E ±2 km, probably along a forest road]; 46 males, 73 females, “Sta. 87. Mt Taylor, 11 km NNW Bairnsdale...fragment of Eucalyptus forest, along roadside between grassland, under logs and litter” [37°45'28"S 147°35'55"E ±1 km, possibly along Bullumwaal Road].
Dicranogonus samples from the three localities listed above have recently been located in the Naturalis Biodiversity Center (K. van Dorp, in litt., 17 September 2014), following a long period during which their location was uncertain. The three samples, which I have not examined, presumably contain the holotype and the published paratypes.
The presence or absence of well-defined paranota on diplosegments is usually a genus-level character in Polydesmida. It is remarkable that both character states are found, with no obvious intermediates, in Australian paradoxosomatid specimens with no consistent, diagnosable differences in the gonopod telopodite between the forms with and without paranota (Fig.
Consistent, diagnosable gonopod variations have long been the basis of species-level taxonomy in Polydesmida. Without such variations, species delimitation on purely morphological evidence is hard to justify, especially if the taxonomist has only a limited number of specimens from an incomplete sampling of the distribution of the genus. In the case of Dicranogonus, however, there is abundant material from localities across the genus range. The geographical pattern for presence and absence of paranota (Fig.
However, the five specimens from Buchan (NMV K-10011; Figs
The timing of these losses might be estimated from future genetic work on Dicranogonus. For current taxonomic purposes, I am satisfied that all material I examined can be assigned to D. pix, which is readily diagnosed on gonopod form and body size and colour.
I thank Graham Milledge (Australian Museum) and Peter Lillywhite (Museum Victoria) for the loan of specimens, and Karsten Goemann (University of Tasmania) for assistance with SEM work. Roy Vogelpoel (in litt., 3 January 2010) kindly corrected the locality for QVM specimen lot 23:25149 from “Charter Island” to “Mt Chappell Island”, 43 years after he had collected Dicranogonus there. I am especially grateful to Ben Brugge (Zoological Museum, Amsterdam) and Karen van Dorp (Naturalis Biodiversity Center, Leiden) for their patience in dealing with the frustrating issue of Jeekel millipede types, and to Sancia van der Meij (Naturalis Biodiversity Center, Leiden) for permission to reproduce Fig. 4 in
Data table
Data type: CSV file.
Explanation note: Known specimen lots of Dicranogonus pix Jeekel, 1982 as of 17 September 2014.