Orthorhachis Jeekel, 1985

Mesibov, Robert, 2008, The millipede genera Gephyrodesmus Jeekel, 1983 and Orthorhachis Jeekel, 1985 in southeastern Australia, a new Lissodesmus Chamberlin, 1920 from Victoria, and observations on male leg setae, spinnerets and metatergite sculpture (Diplopoda: Polydesmida: Dalodesmidae), Zootaxa 1790, pp. 1-52 : 19-20

Orthorhachis Jeekel, 1985

Orthorhachis Jeekel, 1985:51 . Shelley et al., 2000:118.

Type species: O. pallida Jeekel, 1985 , by original designation.

Diagnosis: H+20 Dalodesmidae with tarsus 1.2–2.0 times as long as prefemur, forked tips or a mid-length branch on brush setae, and gonopod telopodite divided into two small branches: a lateral solenomere and a medial process not reaching as far distally as the solenomere tip (except in O. vinnula n. sp.). Distinguished from Tasmanodesmus by the presence in the latter of a third telopodite process lateral to the solenomere and by the presence in Orthorhachis of low, discrete, raised areas on the metatergites. Distinguished from Gephyrodesmus by the branching into solenomere and medial process beginning at more than half the telopodite height in Orthorhachis , and at one-third or less the telopodite height in Gephyrodesmus .

Description: Head with frons and vertex moderately setose, vertex less so; vertigial sulcus usually distinct, reaching to about two-thirds the distance from top of vertex to top of antennal sockets. Tergite widths usually increasing from rings 2 to 5 or 6, about equal from 5 or 6 to17; tergite 3 usually shorter than 2 or 4. Waist usually without longitudinal striations; limbus composed of long, narrow, flat tabs with irregularly toothed ends. Metatergites and paranota with low, discrete, raised areas in Patterns A or B (see metatergite sculpture section, above). Paranota with anterior margin slightly upturned and partly roughened; lateral margin dipping anteriorly in lateral view, usually with a few small notches on midbody rings, each with a minute seta on anterior corner of notch; posterior paranotal corners weakly produced as broad, bluntly rounded projections, flat in lateral view, the projections increasing slightly in length from anterior to posterior; posterior margin minutely and irregularly serrate. Spiracles small, openings round or slightly elliptical, only slightly raised above pleural surface; on diplosegments with anterior spiracle just anterior of coxal midline above a small projecting shelf of cuticle, posterior spiracle about midway between leg-bases. Pore formula 5, 7, 9, 10, 12, 13, 15–19; ozopore opening dorsolaterally close to paranotal margin and just lateral to raised areas, usually near posterior corner at three-quarters to seven-eighths the length of paranotum. Sternites sparsely setose, slightly wider than long or as wide as long, transverse impression deeper than longitudinal ( Fig. 4A). Legs ( Figs. 5C, 5D, 5E) slender; prefemur swollen dorsally, femur slightly so, swelling greatest on anterior legs; tarsus long, thin, slightly curved; relative podomere lengths tarsus>femur>prefemur>(postfemur, tibia). Numerous sphaerotrichomes on tarsus and tibia of anterior legs, hemispherical with sharp-pointed, tapered setal shaft inclined distally and slightly outwards. Preanal ring sparsely setose; hypoproct paraboloid or trapezoidal with rounded corners; epiproct bluntly rounded, extending past anal valves. Male with small gonopore opening ventrally on swelling of leg 2 coxa, not on prominent raised cone. Gonocoxae setose distally on anterolateral and posteromedial surfaces, somewhat concave medially, weakly joined anteromedially. Cannula prominent, inserting anteromedially on telopodite. Telopodites short, when retracted extending to leg 6 coxae; leg 7 coxae well separated, leg 6 coxae much less so. Prostatic groove running laterodistally on anterior surface of telopodite base before curving distally, then laterodistally and following solenomere to tip.

Distribution: Forest and woodland in higher-rainfall areas of southeastern Australia, from central Victoria to southeastern Queensland ( Figs. 31, 32)

Remarks: The gender of the genus is feminine. In Jeekel (1985) the type species name pallida is spelled correctly in the main text but incorrectly pallidus in the caption to figures (p. 53).

Orthorhachis as here circumscribed is a heterogeneous taxon with several species, e.g. O. durabilis n. sp. and O. weiri n. sp., looking very unlike the type species in non-gonopodal features. I am reluctant to erect new genera for such species at this time, given the overall uniformity in gonopod structure in the 18 species included below. Relationships within Orthorhachis may become clearer in future when genetic studies of the group are carried out.

The median tab on posterior sternites ( Figs. 4A, 4B) is an interesting synapomorphy of O. catherinae n. sp., O. paradoxalis Jeekel, 2006 and O. tallagandensis n. sp. The three species all occur in the same part of New South Wales and further collecting may show that they are parapatric. Whether a fourth species from the area, O. cavatica Jeekel, 2006 , also has this character is not yet known. Jeekel (2006) does not mention sternite cones or tabs in his descriptions of either O. cavatica or O. paradoxalis , and I was unable to examine the O. cavatica types.