Theliderma sparsa

Placed in the genus Theliderma following Williams et al. (2017). Theliderma was not recognized by Turgeon et al. (1998) but was resurrected from synonymy by Graf and Cummings (2007) to accommodate a monophyletic clade of five species recognized by Turgeon et al. (1998) under Quadrula (Q. cylindrica, Q. intermedia, Q. metanevra, Q. sparsa, and Q. stapes; see Serb et al. 2003). Theliderma is the oldest available name for this clade and has T. metanevra as its type species. Williams et al. (2017) recognize placement of all five of these species in Theliderma.

Distributional records became confused when Ortmann (1914; 1918) lumped Quadrula sparsa and Quadrula tuberosa under Quadrula intermedia (Bogan and Parmalee 1983, Parmalee and Bogan 1998). Historical records for Q. tuberosa from the Cumberland River are therefore also included with historical records for Q. sparsa (USFWS 1984) but if these are distinct species, then Q. sparsa was not present in the headwaters of the Cumberland River (Parmalee and Bogan 1998).

This species has been reduced to one or two populations in only two rivers that continue to be threatened by alteration of habitat and poor land use practices that increase the transport of silt and pollution. Viability is questionable at the few remaining sites.

Historically, this species was thought to have been widespread in the tributaries of the upper Tennessee and Cumberland river systems (including the Tennessee River, Holston River, Powell River, Clinch River, Cumberland River, Big South Fork Cumberland River, and Caney Fork) (USFWS, 1984). Distributional records became confused when Ortmann (1914; 1918) lumped Quadrula sparsa and Quadrula tuberosa under Quadrula intermedia (Bogan and Parmalee, 1983; Parmalee and Bogan, 1998). Historical records for Q. tuberosa from the Cumberland River are therefore also included with historical records for Q. sparsa (USFWS, 1984) but if these are distinct species, then Q. sparsa was not present in the headwaters of the Cumberland River and they can be attributed to Q. tuberosa (Parmalee and Bogan, 1998). Parmalee and Bogan (1998) claim the only confirmed records from Tennessee are from the Holston River, the upper Powell River (Claiborne and Hancock Cos.), and the unimpounded portion of the Clinch River above Norris Dam. Currently, it is restricted to free-flowing reaches of the upper Powell and Clinch Rivers above Norris Reservoir in (Hancock and Claiborne Cos.) Tennessee (USFWS, 1984; Parmalee and Bogan, 1998) and in one section of the Powell and Clinch rivers in Virginia (Neves, 1991; Ahlstedt, 1991) but has nearly disappeared from this latter locality (Parmalee and Bogan, 1998). Recent archaeological records have shown this species occurrence at Muscle Shoals and Hobbs Island in Madison Co., Alabama, but it is now extirpated from that state (Mirarchi et al., 2004; in appendix 1.2 published separately; Williams et al., 2008), as well as archaeological specimens from the lower Clinch River in Roane Co., Tennessee and Hiwassee River in Bradley Co., Tennessee (Parmalee and Bogan, 1998).

Probably two or three occurrences remain (USFWS, 1984) in the Holston, Clinch, and upper Powell Rivers. The population in the Clinch River (between Cleveland and Craft Mill, Virginia) is of questionable viability due to low numbers and isolated distribution (Neves, 1991; Parmalee and Bogan, 1998). The population in the upper Powell River (about a 40-50 mile stretch above Norris Reservoir), Claiborne and Hancock Cos., Tennessee has nearly disappeared and all remaining populations in Tennessee are extirpated (Parmalee and Bogan, 1998). It appears since 1989, range in the Powell River has declined by 19.4 linear km and overall the species occurs in portions of a 100 km reach of the river, however age studies indicate little recruitment outside a small 0.8 km linear stretch of the river in recent years (Johnson, 2011).

Threats and causes of decline listed in the recovery plan (USFWS, 1984) include impoundment (for flood control, navigation, hydroelectric power, and recreation), siltation (due to strip mining, coal washing, dredging, farming, logging, and road construction), and pollution (municipal, agricultural, and industrial waste discharges, chemical spills) (USFWS, 1984).