Orthorhachis vinnula, Mesibov, 2008

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 : 43-44

Orthorhachis vinnula n. sp.

Fig. 28; map Fig. 31

Holotype: Male. Bennison Plains , Vic, 37º23'13"S 146º43'44"E, 1310 m (GE), 21 April 2008, R. Mesibov and T. Moule, under fallen bark in eucalypt woodland. In MV, K-10690.

Paratypes: In MV: 7 males, details as for holotype, K-10691–10697 ; 7 females, details as for holotype, K- 10698–10704.

Other material examined: None available.

Diagnosis: Gonopod telopodite with solenomere strongly bent posteriorly, tip not reaching as far distally as medial branch.

Description: As for the genus. Male/female approximate measurements: length 19/ 19 mm, midbody prozonite diameter 1.8/2.0 mm, midbody width across paranota 2.6/ 2.8 mm. Live animals near-uniform brownish-grey in body colour with reddish legs; the red pigmentation fades quickly in alcohol. Antennal sockets separated by 2X a socket diameter. Antennae slender, relative lengths of antennomeres 3>(2,5)>4>6. Collum D-shaped, as wide as head and narrower than tergite 2. Metatergite sculpture indistinct, Pattern A. Paranota with anterior margin sloping posterolaterally to more or less distinct corner, lateral margin very slightly convex. Legs slender, leg 6 tarsus 1.9X as long as femur. Brush setae with forked tips.

Gonopod aperture one-third the width of the ring 7 prozonite, flattened-ovate, wider than long, anterior edge longest and nearly straight, rim raised posterolaterally. Telopodite ( Fig. 28) short, base slightly produced anteriorly and medially, telopodite above base wider mediolaterally than anteroposteriorly, abruptly narrowing medially at just under one-half telopodite height; branching beginning at more than three-quarters telopodite height; long setae on posterolateral surface to about one-third telopodite height. Solenomere directed posteriorly, then abruptly bending distally and slightly laterally and narrowing, then tapering to a point while curving slightly medially. Medial process very closely applied to solenomere base, much wider than solenomere, mediolaterally flattened, directed posterodistally and terminating in two projections separated by a wide, shallow notch: distal projection narrowly triangular, apex pointed, terminating distal to solenomere tip; posterior projection with bluntly rounded tip, extending just posterior to distally directed portion of solenomere and curving slightly laterally.

Female slightly larger than male, legs not swollen. Genital aperture with posterior margin slightly raised, directed anteroventrally and with a median triangular projection. Cyphopods not examined.

Distribution: Known only from the Bennison Plains in the eastern Victorian highlands, north of Licola ( Fig. 31).

Etymology: Latin vinnulus, delightful, adjective, for the abundance of specimens at the type locality and the ease with which they were collected (see Remarks).

Remarks: Eucalypt woodland on the Bennison Plains was burned in a wildfire in the austral summer of 2006–2007, and recovering trees subsequently shed long strips and sheets of bark. My wife and I found mature males, females and copulating pairs of O. vinnula under many of these bark pieces, which were lying flat on the ground. We saw no juveniles either on the underside of the bark pieces or on the ground covered by the bark, and it therefore seems likely that the adults were sheltering for the day after wandering at night to disperse or find mates. When disturbed, the animals ran quickly over the bark surface. O. vinnula was very abundant at the collecting site and at another we visited, several hundred metres distant. We would have collected many more specimens if I had not mistaken this species in the field for the superficially very similar Gephyrodesmus arcuatus .