Bromodesmus, Mesibov, Robert, 2004

Mesibov, Robert, 2004, A new genus and four new species of millipedes from Tasmania, Australia (Diplopoda: Polydesmida: Dalodesmidae), with notes on male leg setae in some Tasmanian dalodesmids, Zootaxa 558, pp. 1-19 : 4-8

Bromodesmus n. gen.

Type species: Bromodesmus catrionae n. sp., by present designation.

Other assigned species: Bromodesmus militaris , Bromodesmus riparius and Bromodesmus rufus n. spp.

Diagnosis: Small to medium­sized burrowing dalodesmids ( Fig. 2 ) with head + 20 segments and greatly reduced paranota. Gonopod telopodite straight, slender, greatly expanded at distal end into a posteriorly concave ‘hood’ fringed with teeth; solenomerite arising mesally one­third to halfway along the telopodite, curving anteriorly, then posteriorly, and tapering to a fine point.

Description: Head with moderately deep impressions ventrolateral of antennal bases; bases separated by about twice a socket diameter; vertigial sulcus not deeply impressed but marked by dark pigment; head moderately setose with moderately long setae on clypeus and frons, and a few long setae on the lower portion of the vertex. Antennae ( Fig. 4 A) slender, with antennomeres 2 and 3 subequal in length, longer than 4 and 5 and slightly longer than 6; antennomere 6 the widest. Collum slightly narrower than head and second segment; anterior and posterior margins straight, corners rounded; sparsely setose, principally near the margins. Segments with well­defined waist (= constriction incorporating posterior portion of prozonite, suture and anterior portion of metazonite) ( Fig. 4 B); paranotal development variable (see species descriptions) but lateral margin of paranotum on segment 2 always well below collum corner, lateral margin of paranota on segment 3 just above level of collum corner. Segment surfaces smooth; a few small setae near the waist and the posterior margin of the metazonite; limbus a comb of fine, straight teeth. Ozopore small, opening mid­laterally near posterior edge of metazonite, at the level of the paranotal thickening on segments 5, 7, 9, 10, 12, 13, 15–19. Sternites a little longer than wide, cross impressions well­defined. Anterior legs ( Fig. 4 D) with swollen podomeres, prefemur strongly arched dorsally; posterior legs ( Fig. 4 E) less swollen; tarsus about as long as next longest podomere, the femur. Sphaerotrichomes on tibia and tarsus of leg 3 to penultimate leg; sphaerotrichome shafts with expanded tips ( Fig. 1 B). Dense ‘brushes’ of setae ventrally on prefemur, femur, postfemur and tibia of most legs; ‘brush’ setae with expanded tips ( Fig. 1 E). Leg 2 coxa somewhat extended mesally, genital opening a simple pit on this extension. Legpair 4 not separated at bases, legpair 5 slightly separated, legpairs 6 and 7 well­separated; flexed gonopod telopodites reaching to legpair 5. Spiracle simple in structure with slightly raised rim; on diplosegments, anterior spiracle just above and anterior to anterior leg, posterior spiracle just above and posterior to anterior leg. Preanal ring moderately setose; epiproct tapering to blunt, somewhat rounded tip extending well past anal valves; hypoproct paraboloid or (in B. rufus n. sp.) trapezoidal.

Gonopod aperture ovoid, wider than long, about one­third the width of segment 7 prozonite, with posterolateral portions of rim projecting ventrally. Gonocoxa more or less conical, tapering distally, but with broad, shallow excavation on posteromesal surface ( Fig. 6 ), excavation lined with short setae; gonocoxae very lightly joined mesally near base. Cannula prominent ( Fig. 6 ). Telopodite ( Fig. 5 ) straight, slender; tip expanded into posteriorly concave ‘hood’ with toothed rim; moderately setose with long setae on posterior surface to one­third to one­half the telopodite length; solenomerite arising mesally at one­third to half the telopodite length, curved anteriorly, then posteriorly, tapering to fine point, terminating within or just mesal to ‘hood’; prostatic groove running more or less directly on anteromesal side of telopodite to solenomerite tip.

Females ( Figs. 2 , 4 ) larger than males, with same coloring; legs smaller than corresponding male legs and not swollen ( Fig. 4 ); posterior rim of epigynum raised slightly in center; cyphopods not examined.

Etymology: Greek bromos, stench, + ­ desmus, commonly used combining form in generic names of Polydesmida ; gender masculine.

Remarks: The muscles and some subcuticular tissues of specimens of B. catrionae n. sp., B. militaris n. sp. and B. rufus n. sp. are stained a dark red­brown after long storage in alcohol. It seems likely that the staining is due to a chemically reactive component or components in the defensive secretion. Similar staining can occur in alcohol­preserved specimens of Julida, Spirobolida and Spirostreptida as a result of the tanning action of 1,4­ benzoquinones in the defensive secretion ( Huth 2000). However, the Bromodesmus spp. secretion is unlikely to be a benzoquinone, as it is far more volatile than the secretion of Tasmanian spirostreptidans and has a very different odor. Further, the supernatant alcohol in vials containing long­preserved Bromodesmus spp. is colorless, whereas the liquid in Spirostreptida­containing vials is a deep reddish­purple.

Alcohol­preserved Bromodesmus specimens are also noticeably more brittle than other Tasmanian dalodesmids preserved in the same way for the same length of time. This brittleness is likely to be due to greater calcification of the cuticle, as the cuticle of preserved specimens can be made flexible by soaking in household vinegar.

Figures

FIGURE 2. Bromodesmus spp. females. (A) B. catrionae n. sp. (QVM 23: 22082), (B) B. militaris n. sp. (QVM 23: 15150), (C) B. riparius n. sp. (QVM 23: 45813) and (D) B. rufus n. sp. (QVM 23: 40519). Scale bar = 10 mm.

FIGURE 4. Bromodesmus catrionae n. sp., male and female from the same site on Ballroom Hill (male from QVM 23: 22072, female from QVM 23: 22082). (A) male antenna; (B) dorsal and (C) posterior outlines of segment 12 of male (top) and female (bottom); (D) posterior leg on segment 6 of male (top) and female (bottom); (E) posterior leg on segment 12 of male (top) and female (bottom). Setation and antennal cones not shown. Scale bar = 1.0 mm.

FIGURE 5. Bromodesmus catrionae n. sp. (Left) SEM view of gonopods in situ (QVM 23: 22076). Note that the shapes of the ‘ hoods’ and the solenomerite tips have been somewhat distorted in preparing the specimen for electron microscopy. Scale bar = 0.50 mm. (Right) Mesal view of distal portion of right telopodite (QVM 23: 16185). Dashed line shows course of prostatic groove; for clarity the continuation of the groove to the tip of the solenomerite is not indicated.

FIGURE 6. Bromodesmus catrionae n. sp. SEM view of gonopods removed from segment 7, showing dorsal (posterior) aspect of gonocoxae (QVM 23: 17836); c = cannula. Scale bar = 0.50 mm.