Medionidus acutissimus

Simpson (1914) and Ortmann (1924) recognized Medionidus parvulus as distinct from Medionidus acutisssimus. Van der Schalie (1938) noted that they integrated. Johnson (1977) synonymized M. parvulus with M. acutissimus. Genetic analysis is needed to determine the proper identification of some populations (e.g., Medionidus specimens from the Conasauga River). The relationship of Medionidus acutissimus to Medionidus parvulus is unclear as the two overlap in shell morphology in parts of their ranges. Further taxonomic questions exist as to the relationship between Mobile Basin M. acutissimus and what appears to be that species in the Choctawhatchee, Yellow, and Escambia drainages as slight conchological differences exist. M. acutissimus from the Escambia, Yellow, and Choctawhatchee River drainages are also similar morphologically to Medionidus penicillatus and some authors have included those populations in the range of M. penicillatus (Johnson, 1977; Butler, 1990; Williams and Butler, 1994), but those populations are included in the range of M. acutissimus by Williams et al. (2008) because faunal distribution patterns suggest that faunas in the Choctawhatchee, Yellow, and Escambia River drainages are more closely related to those of the Mobile Basin than those of the Apalachicola Basin.

This is a declining regionally endemic species that could face severe decline or extinction from further loss or degradation of habitat. Although the population in the Sipsey Fork appears to be stable, trends in other populations are towards decline or are not known. It has disappeared from a significant portion of its historical range, including much of southern Alabama and apparently all of the Florida panhandle.

The type locality for Medionidus acutissimus is the Alabama River, Alabama. Historically, it was known from the Alabama, Tombigbee, Black Warrior, Cahaba, and Coosa Rivers and their tributaries in Alabama, Mississippi, Georgia, and Tennessee (USFWS, 2004). Additional records include the Alabama River, Tombigbee River and tributaries (Luxapalila Creek, Buttahatchie and Sipsey Rivers), Black Warrior River and tributaries (Mulberry Fork, Brushy Creek), Cahaba River, and Coosa River and tributaries (Talladega, Choccolocco Creeks, Chatooga River). The current range of the species includes the Luxapalila Creek, Buttahatchie and Sipsey Rivers in the Tombigbee River drainage; the headwaters of the Sipsey Fork (Brushy Creek) in the Black Warrior River drainage; and the Conasauga River (USFWS, 1993). Mirarchi et al. (2004) lists distribution as throughout the Mobile basin in Alabama, Georgia, Mississippi, and Tennessee (see Parmalee and Bogan, 1998) with specimens from the Gulf Coast drainages west of Apalachicola Basin, tentatively identified (potentially these are an undescribed species). It also occurs in the Tombigbee drainage in Mississippi (Jones et al., 2005). McGregor et al. (2000) reported it as absent from the Cahaba River, Alabama. I t is known only from 6 historical sites in the Choctawhatchee River drainage of Alabama and Florida (Blalock-Herod et al., 2005).

At least four river drainages (Mobile, Escambia, Yellow, Choctawhatchee), each of which originally may have constituted one principal "occurrence." Historically, it was widespread throughout theMobile basin; now it occurs sporadically in low numbers with the best populations occurring in the Sipsey Fork drainage. It survives in the Tombigbee River tributaries (Blue Mountain Creek, Luxapalila Creek, Yellow Creek, Buttahatchee River, Sipsey Creek, Lubbub Creek, and Sipsey River), Black Warrior River tributaries (Sipsey Fork and tributaries), and Holly Creek in the Coosa River drainage (USFWS, 2004). It is known from 6 historical sites only in the Choctawhatchee River drainage of Alabama and Florida; recent surveys of these and several other sites in the drainage failed to find any specimens (Blalock-Herod et al., 2005). The species has been reported recently from the Conasauga River inside and adjacent to the Cherokee and Chattahoochee National Forests, Polk Co., Tennessee; as well as Holly Creek, adjacent to the Chattahoochee National Forest, Murray Co., Georgia (Parmalee and Bogan, 1998; Johnson et al., 2005). In the Coosa River basin in Georgia, it is known historically from the Coosa, Etowah, Oostanaula, and Conasauga River drainages but has not been collected live recently (Williams and Hughes, 1998). Johnson and Ahlstedt (2005) located specimens in 2005 in the Luxapallila drainage on the Mississippi/Alabama border. It has likely been recently been extirpated from the Escambia and Yellow River drainages in Alabama and Florida (Williams et al., 2000). Overall in Alabama, it is extant in isolated and widely separated localities in the Mobile Basin and has not been collected from other Gulf Coast drainages since the 1960s (Williams et al., 2008).

Habitat modification, sedimentation, and water quality degradation represent the major threats to this species; it may also be threatened by overutilization for commercial, recreational, scientific or educational purposes as well as disease and predation (USFWS, 1993; 2000). Disappearance from significant portions of its range are primarily due to changes in river and stream channels resulting from dams, dredging, or mining, and historic or episodic pollution events. The species is not known to survive in impounded waters, and more than 1700 km of large and small river habitat in the Basin (Mobile) have been impounded by dams for navigation, flood control, water supply, and/or hydroelectric production (USFWS, 2004).

From USFWS (2000):
In the Mobile River basin, the greatest threats are dams (for navigation, water supply, electricity, recreation, and flood control), channelization (causing accelerated erosion and altered depth; and loss of habitat diversity, substrate stability, and riparian canopy), dredging (for navigation or gravel mining), mining (for coal, sand, gravel, or gold) in locally concentrated areas, point-source pollution (industrial waste effluent, sewage treatment plants, carpet and fabric mills, paper mills and refineries in mainstem rivers), and non-point-source pollution (construction, agriculture, silviculture, and urbanization).