CAMBALIDAE - undet. sp. - undescribed species?
Undet. genus and sp./undescribed species?
Size: Unknown; no complete specimen available.
Group Guild Status
Troglobiont Scavenger Rare
The determination that this species belongs to the family Cambalidae in the order Spirostreptida was made from parts salvaged from the first animal found (Photo 1). This troglobitic millipede is only known from a couple of areas in the cave, including a small area in the Mud Flats and the vicinity of the Fallen Giant formation at the east end of the Big Room (three individuals), and from a single animal found in the west end of the Anticipation Room just southeast of Main Corridor. Only these four individuals have been found and unfortunately, all were dead when found. All four appear to have been adults, and all of them had died on wet (active), off-white colored calcite formations. Three were found on the side of stalagmites (Big Room in the vicinity of the Fallen Giant, and in a small room to the east; the Millipede Tomb Room), and one on the basal apron of a stalagmite (Anticipation Room). Three of the four millipedes were found in an apparently characteristic death pose, with the anterior portion (most) of the body length in a loose coil, with only the posterior portion of the body coming off the coil. The trailing segments of the body apparently relax off a full-coil position when the animal dies.
The species is totally eyeless and appears to be mostly (or entirely) de-pigmented, the body color (based on dead material), being remarkably similar to the off-white color of the formations on which all four carcasses have been found. The single partial specimen we sampled consists of approximately the first two dozen body segments. The specimen we have is female, and at least one intact adult male animal will be needed before the species can be described.
In the absence of live animals, one of the first questions that comes to mind is how long had the bodies of these millipedes been in the location where they had died? It is difficult to assess how long dead millipedes would retain their shape and remain recognizable in such a wet environment. Intuitively one would assume they might last for a year or two (at most) before decay and disarticulation would render them unrecognizable. Considering that three of the animals were found on a near-vertical surface and that they may be subject to movement of water sheeting down the sides of the stalagmites, it would seem logical that they would not persist in these situations for long. However, the third animal found was totally encased in calcite (Photo 3), but could be easily recognized by its configuration as described above. The small room where this (and one other) of the animals was found was appropriately named the Millipede Tomb Room by Esty Pape.
The last of the four was found lying upside down, fully stretched out and partially embedded in the flowstone surface (Photo 4). The last two finds significantly change the perspective on both the method of preservation and a determination of time since death of the animals. It seems that the chitinous exoskeleton of the animals may be highly resistant to decay and/or there is enough surface adhesion between the carcasses (of very low mass) and the damp/wet side of the stalagmite such that their bodies cling to the formation. While these formations may be wet much of the year the actual volume of water sheeting down their sides may be inadequate to dislodge the carcasses. And, once the carcass is attached to the formation by the slightest calcium deposit it is likely to remain in place, and may eventually become totally encased. So the age of these animal remains could be much older than we originally suspected. We do not have a calcite deposition rate for the formation with the entombed millipede so we can not effectively estimate the time since death. RBP has observed significant calcite deposition on active formations in some caves in the southwest (including southern Arizona caves), enough to have covered the observed millipede in 15-20 years. This is, of course, a very crude estimate, and would assume a deposition rate in the higher end of the range of accumulation potential in such situations.
We suspect that the ecology of this species may be tied to the annual summer monsoon rain response in the cave, and that the animals are primarily active at that time, although we have no evidence at this time to support this idea. The species may feed on a bio-film that exists on the surface of calcite formations. Or, like some Polydesmid millipedes, they may be spending most of their life in the soil/mud of the floors of the cave. Their presence above the surface may be seasonal, or even a rare event, which also could explain why they had not previously been observed.
Since all four of the records we have of this species are from identical habitat, we suspect that the animals are somehow closely associated with active (wet) calcite formations during some part of their life cycle. If the animals are dependent on bio-films that develop on actively growing formations, which are supported by regular infiltration of autogenic meteoric waters, an extended period of drought could conceivably reduce available habitat to a level that is unsustainable for the population. Southeast Arizona has been in an extended drought since 1999 (about 15 years; Breshears et al. 2005), and this coincides with the above-mentioned (crude) estimate for an assumed age of the two most recent (non-embedded) of the four millipede carcasses found. It is possible that the species is no longer extant in the cave, these remnants are all that remain, and it is just coincidence that the recent study found the last remains of the species. We hope that this is not the case, and that at some point we will find live animals in the cave.
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