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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
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.
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.
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