A new and unusual species of Amastigogonus Brölemann, 1913 from Tasmania, Australia (Diplopoda, Spirostreptida, Iulomorphidae)

Abstract Amastigogonus insularis sp. n. is described from Schouten and Tasman Islands off the east coast of Tasmania, and a key is presented for the identification of males of Tasmanian Amastigogonus species. The new species differs from the 10 previously described species of Amastigogonus in having a reduced coxite process on the anterior gonopod.


Introduction
In a previous paper (Mesibov 2017) I reviewed the endemic Tasmanian genus Amastigogonus Brölemann, 1913 and added six new species. In all but one of the 10 known Amastigogonus species, the telopodite on the anterior gonopod is slightly longer than the coxite process (Fig. 1A). The latter is typically flattened with a slight lateral concavity, and faces the medial side of the telopodite so that the two structures form a "bird's beak" in which the pseudoflagellum is partly protected. The coxite process in A. danpicola Mesibov, 2017 deviates from this pattern in having shallow fossae at the apex and posterobasally.
In this paper I describe a new Amastigogonus species in which the coxite process is reduced (Fig. 1B) and does not protect the pseudoflagellum. The new species has so far only been recorded from two small islands off the Tasmanian east coast.

Materials and methods
Specimens are stored in 80% ethanol in the Queen Victoria Museum and Art Gallery, Launceston, Australia (QVM). Photomicrographs in Fig. 1 are focus-stacked composites made with Zerene Stacker 1.04. Photomicrographs were taken with a Canon EOS 1000D digital SLR camera mounted on a Nikon SMZ800 binocular dissecting microscope equipped with a beam splitter. Measurements were made to the nearest 0.1 mm with the same microscope using an eyepiece grid and a reference scale. The gonopod telopodite illustrated in Fig. 2 was temporarily mounted in 1:1 glycerine:water and imaged using an eyepiece video camera mounted on an Amscope binocular microscope. A preliminary drawing was traced from a printed copy of the image, with details confirmed by microscopic examination of the mounted object. Latitude/longitude figures are given in decimal degrees to four decimal places, together with an estimate of spatial uncertainty. Diagnosis. Male leg 7 coxa not noticeably elongated or distally swollen; coxite process on anterior gonopod much shorter than telopodite, not protecting pseudoflagellum; pseudoflagellum as in A. peninsulensis Mesibov, 2017 but longer, extending just past telopodite tip. Description. As for the genus description (Mesibov 2017, p. 5) with the following details: holotype male with (59+1) rings, 2.0 mm midbody diameter; paratype male with (51+2) rings, 1.6 mm; longest female (in QVM 23:0093) with (63+1) rings, 2.5 mm. Trunk rings dark grey with light annulus posteriorly and irregular, partly annular light markings on prozonite (Fig. 1D); striae on posterior metazonites reaching ca 1/2 ozopore height.
Distribution. Schouten and Tasman Islands off the east coast of Tasmania (Fig. 3). Name. Latin insularis, insular; adjective. Drawing not to scale.

Remarks.
As with the two known males, the Schouten Island females are smaller than their Tasman Island counterparts: (51+2)-(59+1) rings, 1.5-2.3 mm midbody diameter from Schouten Island, (47+2)-(63+1) rings, 2.3-2.7 mm from Tasman Island. Further, the pseudoflagellum tip in the holotype male from Tasman Island is slightly longer, broader and more medially directed than the tip in the Schouten Island paratype. These are minor differences and I regard the two forms as conspecific.
I doubt that A. insularis sp. n. is restricted to its two widely disjunct localities, ca 105 km apart. However, the only iulomorphid so far collected on Forestier and Tasman Peninsulas, just north of Tasman Island (Fig. 3), is A. peninsulensis Mesibov, 2017. Similarly, the only iulomorphid recorded from the Freycinet Peninsula (Fig. 3), just north of Schouten Island, is A. michaelsae Mesibov, 2017. The latter species is also the only iulomorphid known from Maria Island, halfway between Schouten and Tasman Islands (Fig. 3). I suspect that A. insularis sp. n. will be found in future in coastal habitats along the east coast of the Tasmanian mainland, and possibly also on Maria Island. Key to males of Amastigogonus (see figs 6 and 8 in Mesibov (2017), and Fig. 2