2006 SOUTHEASTERN NATURALIST 5(1):53–56 New Distributional Record for Simpsonaias ambigua (Say) (Salamander Mussel; Bivalvia: Unionidae) in the Duck River, Central Tennessee MICHAEL M. GANGLOFF1,* AND GEORGE W. FOLKERTS2 Abstract - Simpsonaias ambigua (salamander mussel) is a small-shelled member of a monotypic unionid genus and the only freshwater mussel reported to be an obligate parasite of amphibians. Recent surveys of the Duck River drainage found no historical or recent records of the salamander mussel, but documented records for 73 other species, including 53 extant taxa. In 2003, a fresh-dead shell of S. ambigua was collected from the Duck River in Humphreys County, TN. Additional specimens were found in June 2005. These specimens represent the only known occurrence of S. ambigua in the Duck or Tennessee River drainages and may represent the only remaining Tennessee population. Simpsonaias ambigua (Say) (salamander mussel) is one of the world’s most unusual unionids because its only known host is not a fish but the mudpuppy Necturus maculosus (Rafinesque). This small, cryptic mussel historically occurred throughout the upper Mississippi River drainage and as far south as the Cumberland River drainage in Tennessee. Simpsonaias ambigua is found almost exclusively beneath large, flat stones, a microhabitat that presumably facilitates contact with its host (Oesch 1995, Parmalee and Bogan 1998). It was historically widespread in riverine habitats ranging from small streams to larger rivers. However, recent surveys have suggested an alarming decline in its numbers across the midwestern United States. Presently, this species is regarded as endangered in Arkansas, Illinois, Michigan, and Missouri, threatened in Wisconsin, and a species of concern in Indiana and Ohio (Cummings and Mayer 1992, Harris et al. 1997). This unusual unionid is not considered endangered by the US Fish and Wildlife Service, although it was listed as a candidate species prior to the dismantling of the candidate species system. Parmalee and Bogan (1998) reported Simpsonaias ambigua only from the Stones River in the Cumberland River drainage in Tennessee. Specimens were collected from the Stones River in 1965 by David Stansbery (Ohio State University Museum of Zoology). Additional records exist for the Cumberland drainage, including a 1961 record from Smith Fork, a tributary of the Caney Fork River, and a 1962 record from the West Fork of the Stones River (Herb Athearn, Museum of Fluviatile Mollusks, Cleveland, TN, unpubl. data). Simpsonaias ambigua has not been found in Tennessee since 1965 and Parmalee and Bogan (1998) considered it extirpated from the state. Tennessee apparently has no official conservation designation for S. ambigua. 1Auburn Natural History Learning Center and Museum, 331 Funchess Hall, Department of Biological Sciences, Auburn University, Auburn, AL 36849. 2Department of Biological Sciences, Auburn University, Auburn, AL 36849-5407. *Corresponding author - Ganglmm@auburn.edu. 54 Southeastern Naturalist Vol. 5, No. 1 A single fresh-dead specimen of S. ambigua was collected along the shoreline of the Duck River on 2 September 2003 at the Dyer Road boat access, 2.4 km east of Tennessee State Highway 13 in Humphreys County (35°55'55.12"N, 87°44'54.22"W; Fig. 1). The specimen was not identified until 2005, when it was detected while cataloguing vouchers in the Auburn University Natural History Learning Center and Museum. After confirming its identity by examining other specimens at the Florida Museum of Natural History (Gainesville, FL) and consulting with other malacologists, the specimen was accessioned and assigned the lot number AUM8898. Only one other unionid shell was included in this initial collection, a fresh-dead Potamilus alatus (Say). A subsequent visit to the site was made (by G.W. Folkerts) on 6 June 2005, and another complete shell and fragments of three other valves were found. These specimens were accessioned into the Auburn University Invertebrate Collection and assigned the lot number AUM9263. The Duck River in the immediate vicinity of the collection site (Duck River Miles 25–26) ranges in width from 50 to 85 m. Substrate at the collection site consists almost entirely of large limestone boulders up to 1.5 m in width, many of which are slab-like. Interstitial substrates ranged from gravel to silt. At the canoe landing, the banks have been stabilized with rip-rap. During the second site visit, S. ambigua shells were found beneath riprap along the river margin. The Duck River drainage in central Tennessee is perhaps North America’s most biodiverse small river system. A recent survey reported > 640 species of fish, amphibians, aquatic invertebrates, plants, and algae in the drainage (Ahlstedt et al. 2004). The Duck River is a critical refuge for many federally protected species and represents one of the few strongholds for other rare unionid taxa. Several unionid surveys have targeted the Duck River over the last 100 years, and chronologically these include the works of Marsh (1885), Figure 1. Map of the Duck River drainage in central Tennessee and the collection locality (filled circle) for AUM8898 and AUM9263, Simpsonaias ambigua. 2006 M.M. Gangloff and G.W. Folkerts 55 Ortmann (1924), van der Schalie (1939, 1973), Isom and Yokley (1968), Ahlstedt (1991), and Schilling and Williams (2002). Although N. maculosus was not reported from the Duck River by Redmond and Scott (1996), they did report it from the Buffalo River, a major tributary of the Duck. Our detection of S. ambigua indicates that N. maculosus is also present in the lower Duck River and that S. ambigua may also occur in the Buffalo River. Most recently, Ahlstedt et al. (2004) reviewed the material collected by the aforementioned surveys and compiled records from museum collections for an astounding total of 73 mussel species from the Duck River drainage. Additionally, their recent survey found extant populations of 53 taxa during the most comprehensive work in the drainage to date. However, their survey did not sample the lower 61 km of the Duck River. Recently, Schilling and Williams (2002) sampled more extensively in the lower Duck and found 32 unionid species, but did not find S. ambigua. Simpsonaias ambigua is a non-distinctive mussel that could be confused with other unionid species (i.e., Lasmigona, Strophitus, Villosa spp.). The shell of AUM8898 is small (27.4 mm length) and thin with indistinct pseudocardinal teeth and a nearly indistinguishable swelling of the hinge line where the lateral teeth are found in other bivalves (Fig. 2). Although the umbos of this specimen are eroded, a faint double-looped beak sculpture is evident near their terminus. The periostracum is tawny yellow brown and rays are absent. The nacre is pinkish-white. The occurrence of Simpsonaias ambigua in the Duck River brings the total number of mussel species known historically and recently from the drainage to 74 and 54 species, respectively. It demonstrates that even well-surveyed drainages may still yield surprising unionid finds. Evaluation of unionid sampling strategies has demonstrated that intensive efforts are often required to detect rare species, especially in species-rich drainages (Strayer and Smith 2003). However, this doesn’t guarantee that all mussel species present at a particular location will be found. We suspect that a more thorough search of the locality where these specimens were found will turn up additional indi- Figure 2. Specimen AUM8898, Simpsonaias ambigua, Duck River, Humphreys County, TN, 2 September 2003, George W. Folkerts collector, shell length = 27.4 mm. Photograph by Lynn Siefferman, Auburn Biological Sciences. 56 Southeastern Naturalist Vol. 5, No. 1 viduals. Future work in the Duck River clearly needs to target the apparently under-surveyed lower 61 km. Additional sampling efforts targeting S. ambigua in the Duck should focus on its specific microhabitats including slablike rocks and ledges where Necturus is likely to occur. Acknowledgments We wish to thank the National Science Foundation and Auburn University’s College of Science and Mathematics for providing financial support to the Auburn University Museum and Natural History Learning Center. Lynn Siefferman (Auburn Biological Sciences) photographed the specimen illustrated in Figure 2. Steven A. Ahlstedt (US Geological Survey, Knoxville,TN), Kevin S. Cummings (Illinois Natural History Survey, Champaign, IL), and James D. Williams (US Geological Survey, Gainesville, FL) examined specimens and confirmed identifications. John Slapcinski (Florida Museum of Natural History, Gainesville) kindly provided access to specimens. Literature Cited Ahlstedt, S.A. 1991. Cumberland mollusk conservation program activity 1: Mussel surveys in six Tennessee Valley streams. Walkerana 5:123–160. Ahlstedt, S.A., J.R. Powell, R.S. Butler, M.T. Fagg, D.W. Hubbs, S.F. Novak, S.R. Palmer, and P.D. Johnson. 2004. 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