Paredrodesmus, Mesibov, Robert, 2003

Mesibov, Robert, 2003, Two new and unusual genera of millipedes (Diplopoda: Polydesmida) from Tasmania, Australia, Zootaxa 368, pp. 1-32 : 8-9

Paredrodesmus n. gen.

Type species: Paredrodesmus taurulus n. sp.

Further assigned species: P. aceriodendron n. sp., P. australis n. sp., P. bicalcar n. sp., P. monticolus n. sp. and P. purpureus n. sp.

Diagnosis: Small, cylindrical dalodesmoids with head + 19 segments and no sphaerotrichomes; a much­reduced paranotum on somite 2 but no trace of a paranotum on more posterior segments; pore formula 5, 7–18. Readily distinguished from the similar and cooccuring dalodesmoid genus Procophorella by the complete absence of paranota on segments posterior to somite 2.

Description: Males 9–12 mm long, 0.8–1.0 mm in maximum vertical diameter. Colour varying between species, and within species ranging from pale (uncoloured) to yellowishtan, or purple ( P. purpureus ). Head with antennal sockets only slightly impressed, variably separated; vertigial sulcus prominent. Antennomere 6 the longest, variably inflated. Collum narrower than head, anterior and posterior margins nearly straight, corners slightly rounded. From above, somite 2 about as wide as collum, somite width increasing slightly and gradually caudad. Somites with variably weak constriction between pro­ and metazonite; a few setae on the anterior margin of the collum and on the pre­anal somite, somite surfaces otherwise free of setae and featureless. Paranotum on somite 2 a slight thickening just below the level of the collum corner; no trace of paranota on more posterior somites. Ozopores ovoid (long axis dorsoventral), opening midlaterally on somites 5, 7–18 ( Fig. 3 ). Sternites a little longer than wide. Leg­pairs 1–7 variably incrassate, more so anteriorly; ventral leg setae short, no sphaerotrichomes on any legs; midbody legs with prefemur, femur about equal in length, tarsus a little longer ( Fig. 6 C). Anterior spiracle on diplosegments directly over anterior leg, posterior spiracle midway between legs. Pre­anal ring lightly setose; hypoproct paraboloid in outline; epiproct ( Fig. 9 ) tapering to a blunt point, extending past the anal valves and with several long setae, in P. bicalcar divided into two large spurs. Genital opening on leg 2 coxa on variably developed projection. Gonopod aperture about half the width of the somite 7 metazonite, a little wider than long, the anterior margin nearly straight. Gonopod coxae enclosed within gonopod cavity and well separated from aperture margins. Coxae rounded, tapering slightly distally, joined along mesal surface forming a variably integral syncoxite. Cannula prominent, inserting in shallow depression in telopodite base. Female slightly longer and stouter than male, waist much less conspicuous; epigynum with posterior rim slightly raised; cyphopods not examined in any species.

Etymology: Greek paredros, sitting beside, + ­ desmus, commonly used ending for generic names of Polydesmida ; masculine gender. So named because specimens in this genus are almost invariably found close together in humus and soil.

Remarks: Paredrodesmus species are remarkably diverse in gonopod structure and in some details of the anterior legs. They are tentatively grouped here as a genus because they are very similar in overall morphology, very different from other known Australian dalodesmoids and geographically coherent. The six named species show almost no variation in gonopod form across individual species ranges. A seventh species is known from a single male collected near Strathgordon, Tasmania, and will be described when more material becomes available. In the Strathgordon specimen and in five of the species described below, the telopodite bears thickened, pointed, peg­like structures, similar to the ‘starker Stifte’ [stout pegs] said by Attems (1940: 446) to be a characteristic feature of the dalodesmid genus Icosidesmus Humbert & de Saussure, 1869. However, in the latter genus the pegs typically occur as clusters midway along the telopodite, while in Paredrodesmus they arise from the telopodite apex. The presence of these structures does not appear to be a good synapomorphy for Icosidesmus and Paredrodesmus .

Figures

FIGURE 3. (Left) Procophorella innupta n. sp., lateral SEM view of mid­body paranotal ledge and ozopore, female, QVM 23: 41469; scale bar = 0.3 mm. (Right) Paredrodesmus bicalcar n. sp., lateral SEM view of mid­body ozopore, male, QVM 23: 41197; scale bar = 0.04 mm.

FIGURE 6. Antennae and legs of Paredrodesmus spp. males. All drawings to same scale, apical cones and setation not shown. (A) Leg 2 of (left to right) P. aceriodendron n. sp., QVM 23: 41165, P. australis n. sp., QVM 23: 41167, P. b i c a l c a r n. sp., QVM 23: 41178, P. monticolus n. sp., QVM 23: 41155, P. p u r p u re u s n. sp., QVM 23: 41524 and P. taurulus n. sp., QVM 23: 41132; (B) antennae of (left) P. b i c a l c a r n. sp., QVM 23: 41178 and (right) P. aceriodendron n. sp., QVM 23: 41165; (C) leg 9 of P. purpureus n. sp., QVM 23: 41524; (D) leg 3 and sternal projection of P. taurulus n. sp., QVM 23: 41132; (E) leg 1 (left, posterior view) and leg 3 and sternal projection (right) of P. b i c a l ­ car n. sp., QVM 23: 41178.

FIGURE 9. Dorsal SEM views of epiprocts of (left) male Paredrodesmus taurulus n. sp., QVM 23: 41140, and (right) male P. b i c a l c a r n. sp., QVM 23: 41197. Scale bar in both cases = 0.5 mm.