A review of the Western Australian keeled millipede genus Boreohesperus (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract A taxonomic review of the endemic Western Australian millipede genus Boreohesperus Shear is presented in which six species are recognized: the type species, Boreohesperus capensis Shear, 1992, from North-West Cape, one new species, Boreohesperus dubitalis, from Barrow Island and four more new species from the Pilbara region, Boreohesperus curiosus, Boreohesperus delicatus, Boreohesperus furcosus and Boreohesperus undulatus. All six species have highly localized distributions, consistent with being short-range endemics. The nomenclature of the branches of the male gonopod is revised.

introduction All native Australian keeled or flat-backed millipedes (Polydesmida: Paradoxosomatidae) belong to the subfamily Australiosomatinae, distinguishable from other subfamilies by the presence of a tubercle (adenostyle) arising near the base and on the medial surface of the femur of the first leg of the male. All but one (Mjoebergodesmus Verhoeff, 1924) Australian genera conform to this definition (Jeekel 1979) and usually the male first leg is incrassate and bears an obvious, well-developed tubercle.
In Western Australia, the described species of paradoxosomatids fall into five genera: Antichiropus Attems, 1911, Boreohesperus Shear, 1992, Helicopodosoma Verhoeff, 1924, Hoplatessara Verhoeff, 1928, and Stygiochiropus Humphreys & Shear, 1993(Attems 1911Humphreys and Shear 1993;Rowe and Sierwald 2006;Shear 1992;Shear and Humphreys 1996;Verhoeff 1924). A single species of Hoplatessara has been recorded from just one locality in Western Australia: the occurrence of this genus in the state remains in doubt and will be discussed in detail in a forthcoming paper on the millipedes of the Great Western Woodlands area of Western Australia (Car and Harvey, unpublished data). Shear (1992) described the genus Boreohesperus and its first known species, B. capensis, based on specimens from Cape Range in Western Australia, where it was collected from cave entrances. He pointed out that these specimens were not modified for cave life but that they merely "found conditions of the caves congenial" (p 777). The genus was tentatively assigned to the tribe Australiosomatini by Shear (1992) on the basis of the structure of the gonopod. He suggested that the presence of only two acropodite branches in Boreohesperus implied a relationship with several eastern and southern Australian genera that have confidently been assigned to the Australiosomatini. At this stage, there is no further evidence suggesting that the placement of Boreohesperus in the Australiosomatini should be revised and the genus is, therefore, still considered the only confirmed representative of the tribe in Western Australia, with the other Western Australian genera, except Hoplatessara, assigned to the tribe Antichiropodini.
There is no standardized terminology for the description of paradoxosomatid gonopods which may be highly modified across different taxa (Jorgensen and Sierwald 2010) and authors over the years have used a number of different terms for the same structures (Rowe and Sierwald 2006). In the majority of publications, these terms have also implied that the various structures of a gonopod are homologous with those of the podomeres of a walking leg, but there has been no research to confirm this suggestion (Mesibov 2005). Shear (1992) described the gonopod of B. capensis as having a short femorite leading into two branches: the long slender solenomerite bearing the sperm canal, and the shorter rod-like tibiotarsus. Jeekel (1968) identified the tibiotarsus as a process arising on the posterior surface of the gonopod, separate from the solenomerite. In Boreohesperus, the structure Shear labeled the tibiotarsus appears to arise on the antero-lateral surface of the acropodite, but he believed this was due to the coiling of the gonopod.
In this paper, we redescribe the genus and describe a new species of Boreohesperus from Barrow Island that extends the limits of the genus. We also report on four additional new paradoxosomatid species from the Pilbara region of Western Australia (Figure 9). In this paper, they are described and have been included in the genus Boreohesperus as they share the same basic gonopod structure with B. capensis, but, in the light of these new discoveries, the labelling of the gonopod branches has become difficult. As for B. capensis, each of these new species has a gonopod that splits into two main branches from a short femorite. We have labeled one branch of the gonopod, the solenomere (S) which is the branch that carries the sperm canal, and was referred to as the solenomerite by Shear (1992). The other branch is called the non-seminiferous branch (NSB) here, and is measured from the centre of the solenomere base (bs) to the tip of that branch. The NSB appears to be an extension of the femorite and seems to be the equivalent of that branch labeled the tibiotarsus by Shear. In this paper, the femorite (F) is measured from the solenomere base (bs) to the distal edge of the prefemur (PF). Other structures which make up the acropodite are referred to only as processes to avoid confusion. Thus, the processes found at the tip of the solenomere are labeled solenomere tip processes (stp); any process on the main body of the solenomere is called a solenomere process (sp); the pointed process arising on the NSB is labeled the 'nsbp', and a separate process arising posteriorly from the base of the gonopod in some species is tagged the 'pp'. This last process is a tibiotarsus in the sense used by Jeekel (1968) but has not been named as such in this paper.

Material and methods
All of the specimens examined for this study are preserved in 75% ethanol, and are lodged in the Western Australian Museum, Perth (WAM). The specimens of the new species described from the Pilbara region were collected during a joint Department of Environment and Conservation and Western Australian Museum survey of the region, as outlined by George et al. (2009).
The specimens were examined with Leica MZ6 and MZ16A stereo microscopes and the images were generated with a Leica MZ16A automontage imaging system using Leica Application Suite Version 3.7.0 software. Images of whole specimens and their dorsal views were captured first. The left gonopod from each specimen was then removed and a set of images of the gonopod from four different orientations (posterior, anterior, medial and lateral) was captured. Descriptions were compiled with the software package DELTA (Dallwitz 1999) mann, 1913, Dicladosomella Jeekel, 1982, Oncocladosoma Jeekel, 1985and Somethus Chamberlin, 1920. Boreohesperus may be distinguished from the other genera by the two main branches of its gonopod arising from a relatively short but distinct femorite (e.g. Fig. 3E). In Dicladosoma, the two thick squat gonopod branches arise from the prefemur, while in the other three genera, the gonopod is split into the two main branches much more deeply than in Boreohesperus, almost to the acropodite base.
Description. Modified from Shear (1992). Twenty body segments, each smooth and unsculptured, with distinct waist between prozonite and metazonite. Transverse sternal cross-impressions deeper than longitudinal. Paranota, if present, small, poorly developed. Normal pore formula. Legs and antennae with no remarkable features. Gonopod with coxa relatively broad and robust; prefemur sub-globose; femorite length approximately one-quarter to one-third of acropodite length; remainder of gonopod split into two branches, a long, slender, slightly undulating seminiferous branch with curving tip, and a shorter, more upright, pointed branch, often with an additional process near its tip.  Diagnosis. Boreohesperus capensis is considerably larger than other species of the genus, measuring approximately 20 mm in length, and 2 mm in mid-body width (Figs  2A-B). Additionally, the solenomere of the gonopod is twisted and undivided at its tip, unlike those of other species, and the non-seminiferous branch of the gonopod in B. capensis lacks the extra process seen in all other species (Figs 1A, 2C-F).
Distribution. This species is restricted to the Cape Range region of Western Australia (Fig. 9). Etymology. This species is named for the shape of the gonopod that is markedly different from those of the other species (curiosus, Latin, adjective, odd, different).
Diagnosis. Boreohesperus curiosus sp. n. has an easily recognizable gonopod in which the solenomere, when seen in medial or lateral view, curves in an arc (Figs 3E, F) and ends in two large claw-like processes (Fig. 3D). This species also bears two, small, spine-like processes situated at the tip of the solenomere (Fig. 3E).
Description. Holotype male: Body approximately 7 mm long; mid-body ring approximately 1 mm wide dorsally, with distinct waist between prozonite and metazonite; legs of moderate length, approximately equal to length of 1 to 2 mid-body rings. Colour bleached by alcohol. Paranota on all but first few body rings small. Sternites, other than those of fifth body ring, with no noticeable features. Anterior spiracles at mid-body flat circular. Antennae distinctly clavate, of moderate length, extending approximately to first body ring behind collum (to body segment 2), antennomeres relatively robust (Figs 3A, B). Gonopod long, extending at least to fifth body ring; coxa (C) much broader than acropodite and approximately 2× as long as broad; prefemur (PF) short, sub-globose; femorite (F) short, one-quarter to one-third length of acropodite, slightly narrower at base, then broadening; non-seminiferous branch (NSB) broadest at solenomere base, then narrowing to form blunt finger shape; process on medial surface of NSB (nsbp) sharply pointed, arising close to NSB tip, and slightly shorter (approximately two-thirds length) than NSB, extending well beyond rounded branch tip; solenomere (S) relatively long and slender, arising midway between NSB tip and prefemur, basal third curving away from NSB and tip curving back towards gonopod midline to form definite arc; solenomere tip divided into two, main pointed claw like forks, with two small spinelike processes (stp) occurring at base of shorter fork when viewed medially; solenomere process (sp) absent; separate posterior process (pp) absent (Figs 1B, 3C-F).
Female: similar to male, except for genitalic features. Distribution. This species in known only from two specimens found at Mt Elvire in the Pilbara region (Fig. 9).  Etymology. This species is named for its tiny size and delicate gonopods (delicatus, Latin, adjective, dainty).
Diagnosis. This species is most similar to Boreohesperus undulatus sp. n. but the gonopods of the two species differ in the following ways: (1) in B. delicatus sp. n. the femorite and non-seminiferous branch (NSB) together form a relatively narrow boat shape (Figs 4E, F) (Fig. 4C), as in B. undulatus sp. n. (Fig. 8C). Description. Holotype male: Body approximately 7 mm long; mid-body ring approximately 0.75 mm wide dorsally with distinct waist between prozonite and metazonite; legs of moderate length, approximately equal to length of 1 to 2 mid-body rings. Colour bleached by alcohol. Paranota on all but first few body rings small. Sternites, other than those of fifth body ring, with no noticeable features. Anterior spiracles at mid-body flat circular. Antennae distinctly clavate, of moderate length, extending approximately to first body ring behind collum (to body segment 2), antennomeres relatively robust (Figs 4A, B). Gonopod of medium length, extending to posterior edge of fifth body ring; coxa (C) much broader than acropodite and approximately 2× as long as broad; prefemur (PF) short, sub-globose; femorite (F) short, one-quarter to one-third length of acropodite, noticeably narrower at base, then broadening; non-seminiferous branch (NSB) broadest at solenomere base then narrowing to form roughly triangular shape with broadly rounded tip; process on medial surface of NSB (nsbp) slender, arising approximately midway between NSB tip and base of solenomere (bs), similar in length to NSB, extending well beyond branch tip; solenomere (S) relatively long and slender, arising midway between NSB tip and prefemur, forming a distinct 'S' shape when viewed in any orientation; solenomere tip divided into two, main pointed ribbonlike forks, with third small spine-like process (stp) seemingly arising between main forks; solenomere process (sp) absent; separate posterior process (pp) absent (Figs 1C, 4C-F).
Female: Similar to male, except for genitalic features. Distribution. This species is known only from the locality of Marda Pool in the Pilbara Region (Fig. 9) where it was found co-occurring with B. undulatus sp. n..  Etymology. This species is named for the fact that, as the first new species of Boreohesperus to be discovered, there was initial difficulty in deciding on a genus in which to place it (dubitalis, Latin, adjective, to be doubted).

Boreohesperus dubitalis
Diagnosis. This species differs from the four other new species because it is noticeably larger, although it is smaller than B. capensis. In common with B. furcosus sp. n. and B. undulatus sp. n., this species carries a process on the main body of the solenomere of the gonopod, but unlike the other species, this process is long and finger-like, extending almost to the solenomere tip (Fig. 6E).
Description. Holotype male: body approximately 10 mm long; mid-body ring approximately 1.2 mm wide dorsally with distinct waist between prozonite and metazonite; legs of moderate length, approximately equal to the length of 1 to 2 mid-body rings. Colour dark brown overall and legs with coloration similar to that of body. Paranota on all but first few body rings small. Sternites, other than those of the fifth body ring, with no noticeable features. Anterior spiracles at mid-body flat circular. Antennae less obviously clavate, fifth and sixth antennomeres only slightly wider than proximal ones, long, extending beyond body segment 2, antennomeres relatively slender (Figs 5, 6A, B). Gonopod long, extending at least to fifth body ring; coxa (C) much broader than acropodite and approximately 2x as long as broad; prefemur (PF) short, sub-globose; femorite (F) short, one-quarter to one-third length of acropodite, slightly narrower at base, then broadening; non-seminiferous branch (NSB) broadest at solenomere base then narrowing to form pointed finger-like shape; process on medial surface of NSB (nsbp) pointed, arising closer to NSB tip than to solenomere base (bs), and much shorter than NSB; solenomere (S) relatively long and slender, arising midway between NSB tip and prefemur, basal third curving away from NSB and tip curving back towards gonopod midline to form loose arc; solenomere tip divided into two, main pointed ribbon like forks; solenomere process (sp) present, long, finger-like and extending almost to solenomere tip; separate posterior process (pp) arising near solenomere base, long, slender, pointed and approximately half solenomere length (Figs 1D, 6C-F).
Female. Similar to male, except for genitalic features. Distribution. Boreohesperus dubitalis sp. n. is endemic to Barrow Island where it is widespread and abundant (Fig. 9). However, due to its restricted distribution of less than 100 km 2 , it clearly represents a short-range endemic species.
Etymology. This species is named for the solenomere of the gonopod that is more branched than those of other species (furcosus, Latin, adjective, full of forks). Diagnosis. This species may be distinguished from the other small species of Boreohesperus found in the Pilbara by the more upright solenomere and the presence of two processes on the solenomere of the gonopod which are also found in B. curiosus sp. n. and B. undulatus sp. n.. In B. curiosus sp. n., however, these processes arise at the solenomere tip (Fig. 3E) while in B. furcosus sp. n. and B. undulatus sp. n., one process is situated near the solenomere tip and the other occurs approximately one third along the solenomere length from the tip (Figs 7E, 8E). Most importantly, B. furcosus sp. n. lacks the posterior process of B. undulatus sp. n., and has a noticeably long femorite compared with all the other species.
Description. Holotype male: body approximately 8 mm long; mid-body ring approximately 0.75 mm wide dorsally, with distinct waist between prozonite and meta- zonite; legs of moderate length, approximately equal to the length of 1 to 2 mid-body rings. Colour bleached by alcohol. Paranota on all but first few body rings small. Sternites, other than those of fifth body ring, with no noticeable features. Anterior spiracles at mid-body flat circular. Antennae distinctly clavate, long, extending well beyond body segment 2, antennomeres relatively robust (Figs 7A, B).Gonopod long, extending at least to fifth body ring; coxa (C) much broader than acropodite and approximately 2x as long as broad; prefemur (PF) short, sub-globose; femorite approximately half acropodite length, slightly narrower at base, then broadening; non-seminiferous branch (NSB) short, broad with pointed tip; process on medial surface of NSB (nsbp) sharply pointed, arising close to NSB tip, longer than NSB, extending well beyond branch tip; solenomere (S) relatively slender and upright, arising closer to NSB tip than to prefemur;. solenomere tip divided into two, main pointed ribbon like forks, with third small spine like process (stp) arising at base of main forks; solenomere process (sp) present, short; separate posterior process (pp) absent (Figs 1E, 7C-F).
Female: Similar to male, except for genitalic features. Distribution. This species had been found from only one locality, Mt Minnie, in the Pilbara region of Western Australia (Figure 9). Etymology. This species is named for the shape of the gonopods (undulatus, Latin, adjective, wavy).

Boreohesperus undulatus
Diagnosis. This species is similar to B. delicatus sp. n., but the gonopod is slightly larger and the shape of the non-seminiferous branch and femorite together is much broader (spindle shaped) than that of B. delicatus (Fig. 8F). In addition, the gonopod of B. undulatus sp. n. carries a posterior process (Fig. 8C), lacking in B. delicatus sp. n.. The presence of a posterior process also distinguishes this species from B. furcosus sp. n., although B. dubitalis sp. n. also carries this posterior process. B. undulatus sp. n. is, however, much smaller than B. dubitalis sp. n., and the solenomere process found on the male gonopod of B. undulatus sp. n., while present (Fig. 8E), as it is in B. dubitalis sp. n., is much shorter than the relatively long finger-like solenomere process found on B. dubitalis sp. n. (Fig. 6E). Description. Holotype male: body approximately 7 mm long; mid-body ring approximately 0.75 mm wide dorsally with distinct waist between prozonite and metazonite; legs of moderate length, approximately equal to length of 1 to 2 mid-body rings. Colour bleached by alcohol. Paranota on all but first few body rings small. Sternites, other than those of fifth body ring, with no noticeable features. Anterior spiracles at mid-body flat circular. Antennae distinctly clavate, of moderate length, extending approximately to first body ring behind collum (to body segment 2), antennomeres relatively robust. Gonopod long, extending at least to fifth body ring; coxa (C) much broader than acropodite, and approximately 2× as long as broad; prefemur (PF) short, sub-globose; femorite (F) short, one-quarter to one-third length of acropodite; noticeably narrower at base, then broadening; non-seminiferous branch (NSB) noticeably broadest at solenomere base then narrowing to form broad spindle shape with pointed tip; process on medial surface of NSB (nsbp) pointed, arising closer to NSB tip than to solenomere base (sb), and much shorter than NSB, extending just beyond branch tip; solenomere (S) relatively long and slender, arising closer to prefemur than to NSB tip, forming distinct 'S' shape when viewed in any orientation; solenomere tip divided into two, main pointed ribbon like forks, with third small spine-like process (stp) appearing to arise between main forks solenomere process (sp) present, short; separate posterior process (pp) arising near bs, long, slender, pointed and approximately half solenomere length.
Female: Similar to male, except for genitalic features. Distribution. This species has been collected from two localities in the Pilbara: Karratha Station and Marda Pool, situated ca. 50 km apart (Fig 9).

Discussion
With few exceptions, paradoxosomatid millipede species in Australia are considered to be short-range endemics, defined by Harvey (2002) as species with natural distributions of less than 10,000 square kilometres. Most maintain very small ranges, well below Harvey's threshold, for example, species of the genus Dicladosomella in south-western New South Wales (Car 2012) and nearly all species of the genus Antichiropus in Western Australia (Attems 1911). The genus Boreohesperus is confined to Western Australia and, at present, has been found only in a relatively small area of the semiarid region of that state between latitudes 20°30'S and 22°30'S ( Fig. 9). Extensive terrestrial invertebrate surveys have been carried out in Cape Range and the Pilbara region as well as on Barrow Island, and it appears that each paradoxosomatid species, including those of the genus Boreohesperus, has a very limited range, with B. dubitalis sp. n. being endemic to Barrow Island. Boreohesperus delicatus sp. n. and B. undulatus sp. n. are sympatric, both occurring at Marda Pool in the Pilbara and B. curiosus sp. n. and B. furcosus sp. n. have each been found at single localities. The rarity of specimens in the collection of the Western Australian Museum, apart from the two species from the intensively sampled Barrow Island and Cape Range caves, suggests that Boreohesperus species are rarely active on the surface, and may only emerge from the soil after heavy rains.