MACROSTERNODESMIDAE - Nevadesmus sp.? - undescribed species
Nevadesmus ? - undescribed species
Size: 2.94 mm
Group Guild Status
Troglobiont Scavenger Rare
This apparently rare animal was first discovered in the cave on December 12, 2009 when a single adult female was taken from the underside a damp, deteriorating, and somewhat moldy wood shim that was lying on the cave floor near the far west wall of the Big Room. We assume that the shim was an abandoned piece of debris from the original commercial development of the cave. The species is totally de-pigmented and blind, and is a true troglobite. The animal is quite small, about 3 millimeters in length, and ranks among the smaller of the known cave Polydesmida. Some cave millipedes, particularly smaller species of Speodesmus (Polydesmidae) are apparently soil burrowing species (Elliott 2004).
Millipedes may feed on a variety of materials, but many species are primarily saprophagous, feeding on decomposing vegetable debris including wood or other plant parts. A diet of plant materials is low in protein, and millipedes typically feed on these materials when the materials have reached an advanced state of decay. Fungi break down the complex structures of plant materials, reducing toxicity and concentrating nutrients, making them more assimilable to millipedes and other invertebrates (David 2009). Some millipedes will also feed on fecal materials and dead invertebrates (David 2009; RBP, personal observation).
Subsequent to the original discovery of this species we established four invertebrate stations in the same immediate area in hopes of finding additional animals later in the study. As the months went by and the wood blocks at the invertebrate stations began to decay and support a variety of molds, we began to see small invertebrates showing up at these sites. On April 9, 2011 we finally found three juveniles of this millipede on one of the molding wood blocks, approximately 3.5 meters north of the location where the original animal was found. Without the aid of a 10-power hand lens these juvenile animals would certainly have been overlooked, as they were only about 0.5 mm in length. They were found at the edge of a section of dense greenish-gray mold on the underside of the wood block. During the following trip into the cave on May 7, 2011 we found two of these millipedes on the same block. These animals were probably some of the ones observed the previous month. The forest of mold on the block could easily conceal such small animals and the third individual (or others) may have been present, but obscured by the mold.
The taxonomy of cave millipedes is very much in flux, and there is apparently much work that needs to be performed on the group in western North America to settle many of the species, genera, and even families into more coherent groups (Shear et al. 2009). Genetic studies of this group will be immensely helpful in sorting out these taxa, but there is currently little such data available for comparison, and in the interim a continuation of morphological-based species descriptions will have to suffice. Unfortunately, adult males are required to perform morphological descriptions, so the species at Kartchner will have to wait until we are able to obtain additional specimens. At this point we do not know what the population size of the animals is in the cave. Intuitively, based on the few observed animals and their apparent very limited distribution within the cave, they may be quite rare. On the other hand, if it happens that the species has a soil burrowing behavior, we may simply not have found a good way of observing the animals. If they spend most of their time in the soil/mud floors of the cave, and they are capable of surviving on nutrients present there, they may become evident at the surface only when exceptional food sources, such as decaying wood, become available.
There is a bat guano deposit about 8 meters from the area where the millipedes were found, but searches of this deposit revealed none of the animals. The guano deposit appears to get some fresh deposition annually early in the season each year, but the accumulation represents use by only a small number of bats. Rather than being peripherally associated with the ecology of the guano deposit, we suspect that the millipedes are more likely to be cave soil profile inhabitants.
Other invertebrates observed on molding wood at Millipede Meadows include springtails (collembola), mites (acarida), the cave isopod (Brackenridgia), and an occasional nesticid spider (E. pallida).
We will continue to monitor the wood bait invertebrate stations in hopes of finding additional individuals of the species, but additional search methodologies may be required to obtain additional specimens. As with all troglobiotic species, unless populations are obviously robust, sampling needs to be spatiotemporal (constrained by location and time; to preclude population effects resulting from sampling) in nature.
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