Nevadesmus Shear

Shear, William A., Taylor, Steven J., Wynne, Judson & Krejca, Jean K., 2009, Cave millipeds of the United States. VIII. New genera and species of polydesmidan millipeds from caves in the southwestern United States (Diplopoda, Polydesmida, Macrosternodesmidae), Zootaxa 2151, pp. 47-65 : 58-59

Nevadesmus Shear , new genus

Type species: Nevadesmus ophimontis Shear , new species.

Etymology: Named for the state of Nevada, with the combining stem – desmus, traditionally used for the names of polydesmidan millipeds.

Diagnosis: Very small (<5.0 mm length) polydesmidan millipeds with 20 trunk segments, lacking pigment; metatergites ( Fig. 3 ) with three transverse rows of short, brushlike or clavate setae ( Fig. 10 ), rows straight, setae on low pustules. Collum ovoid, narrower than head and slightly narrower than first leg-bearing segment. Paranota low, margins not strongly toothed, posteriolateral angles right-angled to acute, but not produced into processes beyond ozopores ( Figs. 3 , 10 ). Pygidium blunt, nearly hemispherical when viewed dorsally, sparsely setose, with usual four spinnerets (Shear 2008) arranged in a square and set in individual depressions; pygidial process very short, continuing line of pygidium. Males with pregonopodal legs unmodified. Gonopods with coxae globular, fixed, entirely filling gonostome, tightly appressed or fused in midline; prefemora sparsely setose, strongly transverse, articulating with coxae by process fitting into coxal notch. Exomere long, sinuous, arising from distomesal margin of prefemur, endomerite large, distally with three sinuous processes, exceeding other parts of gonopod. Acropodite bulky, solenomere incurved, nearly sessile, opening of seminal canal widened, proximal subtending process widely separated from solenomere, thin, curved, acute; no obvious tibiotarsus.

Nevadesmus differs from all previously known southwestern macrosternodesmids in its small size. It may be distinguished from Sequoiadesmus by its much shorter solenomere.

Distribution: Known from caves in White Pine and Lincoln counties, Nevada.

Notes: This genus is closer in its gonopod to Tidesmus than to Pratherodesmus , particularly in the proportions of prefemoral processes. However, the gonopods most closely resemble those of the much larger Harpogonopus Loomis 1960 , generally accepted as a nearctodesmid ( Shelley 1993, 1994; Shelley & Shear 2006). Though having the general somatic appearance of a macrosternodesmid, the gonopods of species of this genus are quite nearctodesmid-like, with both endomerite and exomere well-developed, but without an obvious tibiotarsus.

It now seems likely, based on size, geographical proximity, and nonsexual characters that “ Tidesmus ” hubbsi Chamberlin 1943 (see Shear & Shelley 2007) is a member of this genus, and it is included here, though males still have not been collected. A female of hubbsi was illustrated by Shear & Shelley 2007, and the history and provenance of the species was discussed therein.

Figures

FIGURES 3 – 6. Segments 10, dorsal view. Fig. 3. Nevadesmus ophimontis. Fig. 2. Pratherodesmus ecclesia. Fig. 3. P. despaini. Fig. 6. P. voylesi.

FIGURES 7 – 10. Figs. 7 – 9. Pygidia, dorsal view. Fig. 7. Nevadesmus ophimontis. Fig. 8. Pratherodesmus despaini. Fig. 9. P. voylesi. Fig. 10. Metazonital setae anterior to ozopore of segment 10, Nevadesmus ophimontis.