Polydesmida species: Paradoxosomatidae
Paradoxosomatidae is the largest family in the millipede order Polydesmida. There are hundreds of species in the mainland States and Territories, but only nine in Tasmania. Two (possibly three) of these are introductions from the mainland. The Dutch myriapodologist C.A.W. Jeekel was planning to describe the three unnamed Tasmanian natives, but died in 2010 before doing so; I hope to publish the names and descriptions in the near future. All our paradoxosomatids are H+20 Polydesmida.
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Aethalosoma solum Jeekel, 2006
Aethalosoma solum grows to ca 25 mm long and is sometimes day-active. It is a Tasmanian endemic and is found in both dry and wet eucalypt forest. In the north of the State its distribution ends at the biogeographical divides known as the Mersey Break and the East Tamar Break.
Akamptogonus novarae (Humbert and de Saussure, 1869)
Akamptogonus novarae is colourfully patterned and grows to ca 20 mm long. It was first collected from a Launceston garden in the 1970s, and in the 2000s it was found in the Royal Tasmanian Botanical Gardens in Hobart and in parkland at Riverside in Launceston. A. novarae is believed to be native to the Australian mainland, but its home range is unknown. Overseas, it has been introduced to New Zealand and the Hawaiian Islands.
Adults of this species are dark brown to black, often with lighter paranota, and reach ca 20 mm in length. Dicranogonus sp. is abundant in the Furneaux Group but only seems to have a 'toehold' distribution in the far northeast of mainland Tasmania. It is day-active and forms 'mating swarms' in spring in coastal heathland. A very similar (possibly the same) Dicranogonus species is abundant in SE Victoria.
Notodesmus scotius Chamberlin, 1920
Adult N. scotius are shiny black or dark chestnut brown and reach ca 20 mm in length. Males are much more slender than females. N. scotius can be very abundant in dry forest and heathland in the Northeast and is often seen wandering in the open during the daytime. Adult males and females can be found copulating in 'mating swarms' during the spring in some areas. Isolated occurrences of N. scotius at Stanley, near Liawenee and at Pumphouse Point (Lake St Clair) suggest to me that this species may be expanding its range with human help. Whether this species is native to Tasmania is still uncertain. An apparently identical Notodesmus is found in Victoria and New South Wales.
Pogonosternum nigrovirgatum (Carl, 1902)
Pogonosternum nigrovirgatum is a common species in southern Victoria and was first found in Trevallyn in 2006. It looks very much like the native Tasmanian Pogonosternum species (below), but the lateral dark bands are a little wider. Neither of the native Pogonosternum species occurs in the central north.
View of right gonopod from centre-line of body, modified from Jeekel (1965)
Undescribed Pogonosternum species
The two native Tasmanian Pogonosternum species reach ca 25 mm in length and live at opposite ends of Bass Strait and the north coast. I have seen Pogonosternum sp. 'NE' wandering in full sun in coastal grassland at Petal Point in September. Pitfall trapping in northeast coastal heathland suggests that this species has a midwinter mating season. Like Dicranogonus sp., Pogonosternum sp. 'NE' is a Furneaux Group millipede with a 'toehold' distribution on the northeast Tasmanian mainland. Pogonosternum sp. 'NW' (illustrated above) seems to be a King Island and Hunter Group species with a 'toehold' distribution in the far Northwest, where it can be found in coastal scrub, swamp forest and wet eucalypt forest at low elevations.
Pogonosternum sp. 'NE'
Pogonosternum sp. 'NW'
Images show side views of tip of left gonopod
Somethus species are also found in South Australia, Victoria and New South Wales. The two Tasmanian species are ca 25 mm long and dark chestnut brown when mature, but juvenile stadia and young adults are light tan. The individual in the image above is halfway between tan and dark brown.
S. mesibovi is restricted to wet forest and scrub in the far Northwest and on King Island and the Hunter Group. S. tasmani is Tasmania's most ecologically tolerant polydesmidan. It occurs in coastal dune scrub, closed tea-tree and swamp forest, eucalypt woodland, dry eucalypt forest, wet eucalypt forest and oldgrowth rainforest from sea level to at least 800 m. It is one of the few Tasmanian polydesmidans found on sandy coastal soils. Although S. mesibovi and S. tasmani have overlapping ranges, they have not yet been found in the same patch of forest. Both species are abundant in Pinus radiata plantations.
The two Somethus species are identical in overall appearance and can only be separated by examining the male gonopods. As shown in the drawing above and the gonopod images below, S. mesibovi has a sharp bend in the solenomere (s), while the solenomere in S. tasmani is more gradually curved.
Somethus mesibovi Jeekel, 2006
Somethus tasmani Jeekel, 2006
Side views of right gonopod