Idagona lehmanensis, Shear, William A., 2007

Shear, William A., 2007, Cave millipeds of the United States. V. The genus Idagona Buckett & Gardner (Chordeumatida, Conotylidae, Idagoninae), Zootaxa 1463, pp. 1-12 : 9-11

Idagona lehmanensis , n. sp.

Figs. 4 , 8, 12-14, 18, 21-23

Types: Male holotype, two male paratypes and female paratype from Water Trough Cave, Great Basin National Park, Nevada, collected 24 May 2006 by S. J. Taylor, J. K. Krejca, M. G. Slay and G. Baker (FMNH). Additional immature specimens were collected at the same time.

Diagnosis; Idagona lehmanensis is easily distinguished from all other known Idagona species by the complicated subterminal branch of the anterior gonopod ( Figs. 21, 22 ) and the presence of modified, porebearing femora on the fourth, as well as the third, legpair ( Fig. 13 ). The tenth coxae of lehmanensis ( Fig. 18 ) have much less well-developed apical knobs and are extended beyond the trochanteral joint; the anterior surfaces are poorly sclerotized and the coxal gland openings are frontal rather than ventral.

Etymology: The species epithet, lehmanensis , was suggested by S. J. Taylor and makes reference to the former Lehman Caves National Monument, which became Great Basin National Park in 1986.

Description: Male ( Fig. 23 ): Length, 13.0 mm, width 1.0 mm. Ocelli 23-27, round, black, in compact oval patch, dorsal row of ocelli somewhat indistinct. Third legpair ( Fig. 12 ) with expanded femur bearing adenostyle as low mound; adenostyle subtended on anterior side by cluster of small, cuticular granules ( Fig. 14 ).

Fourth legpair similar ( Fig. 13 ). Gonopods ( Figs. 4 , 8, 21, 22): anterior gonopods large, upright, distally expanded, with complex posteriorly located subterminal branch ( Figs. 21. 22 ) bearing numerous cuticular fimbriae, narrow bifid subbranch, and distally expanded subbranch. Apex of gonopod deeply divided, medial division broad, trullate; lateral division narrow, evenly curved. Posterior gonopod coxites with poorly sclerotized sternum, basal gonopodal elements much reduced, coxites relatively small, not scooplike, with small posterior nodule, clusters of microteeth near apex. Tenth coxae ( Fig. 18 ) extended beyond trochanteral articulation, posterior knob low, anterior surface poorly sclerotized, membranous, gland opening on anterior surface. Coloration white to pale tan, anterior segments and head lightly mottled purplish-brown, legs white ( Fig. 23 ).

Female similar to male in nonsexual characters.

Distribution: In addition to Water Trough Cave, juvenile idagonines undoubtedly this species were collected in the nearly adjacent Model Cave.

Notes: Idagona lehmanensis differs strongly from the other two species and might have been considered the type of a new genus. However, such designation, if justified, can wait for the discovery of more species of idagonines and a fuller understanding of their relationships. The more complex gonopods of I. lehmanensis , when compared to the other two, mirrors a similar situation in the eastern North American genus Conotyla ( Conotylidae , Conotylinae ), in which species with simpler gonopods are found in the northern part of the generic range, and moving south, one finds gonopods become progressively more complex. The more northerly occurring species of Conotyla are also more widely distributed; southerly species may have ranges restricted to single ridgetops or summits ( Shear 1971). At this point we do not know enough about the diversity or distribution of Idagona to draw a parallel.

The caves of this immediate region are closely clustered and many are isolated from one another only by relatively recently formed erosional features. Idagona lehmanensis very likely will be found in most or all of these caves. As with I. westcotti , the presence of this species, not highly adapted for life underground, in these caves is probably attributable to the latest Pleistocene climatic events: as the Great Basin climate became drier, forested habitats retreated to higher altitudes on the many inselberg ranges ( Vandevender and Spaulding 1979), but because of the significantly more southerly location of the caves, this may have happened much earlier than in northern Utah and southern Idaho. As with the Snake River lava beds, the present surrounding ecosystem is sagebrush desert and dry juniper woodland—inhospitable for chordeumatid millipeds. Besides I. lehmanensis , the two caves also host a new genus and species of polydesmidan milliped, to be described later.

Despite its likely isolation in caves, as with its congeners, little special adaptation can be discerned in this species; indeed the number of ocelli present is considerably greater than that in the two northern species. The Great Basin is a region of North America where crustal extension has resulted in the tipping and downdropping of blocks of strata, producing the characteristic basin-and-range topography. Isolated mountain ranges, many high enough to have forested habitats in the otherwise desertlike or arid grassland terrain, are separated by basins that often have only internal drainage and may harbor short-lived, saline bodies of water. Particularly in eastern Nevada, many of these inselbergs contain karst (Map 1). At higher elevations in Great Basin inselberg ranges, where moist forests occur, relict populations of this or other Idagona species may exist, just as they may in areas of the Rocky Mountains, to the northeast. These habitats in eastern Nevada remain almost entirely unexplored for invertebrate biodiversity, as do the many other karst regions of the state.

Figures

FIGURE 23. Idagona lehmanenesis, n. sp. Anterior end of male paratype. Note the swollen femora on both legpairs 3 and 4 and the absence of conotyliform telopodites on the posterior gonopods. Photo by S. J. Taylor.

FIGURES 1 – 4. Gonopods of Idagona species. 1, Idagona westcotti, Giant Arch Cave, posteriorventral view. 2. I. westcotti, Ice Capades Cave, posterioventral view. 3. I. jasperi, n. sp. posterioventral view. 4. I. lehmanenesis, n. sp., posterior view.

FIGURES 21, 22. Idagona lehmanensis n. sp. 21. Tip of anterior gonopod, ventral view. 22. Tip of anterior gonopod, lateral view.

FIGURES 9 – 14. Pregonopodal leg modifications of Idagona species. 9 – 12, third legs, anterior views. 9. Idagona westcotti, Giant Arch Cave. 10.. I. westcotti, Ice Capades Cave. 11. I. jasperi n. sp. 12. I. lehmanensis n. sp. 13. Leg 4 of I. lehmanensis n. sp., anterior view. 14. Denticles near adenostyle of leg 3 femur of I. lehmanensis n. sp.

FIGURES 15 – 18. Leg 10 coxae of Idagona species, posterior views. 15.. Idagona westcotti, Giant Arch Cave. 16. I. westcotti, Ice Capades Cave. 17. I. jasperi n. sp. 18. I. lehmanensis n. sp., anterior view.