Lithasia spicula, Minton, Russell L., Savarese, Steven P., Jr & Campbell, David C., 2005

Minton, Russell L., Savarese, Steven P., Jr & Campbell, David C., 2005, A new species of “ Lithasia ” (Mollusca: Caenogastropoda: Pleuroceridae) from the Harpeth River, Tennessee, U. S. A., Zootaxa 1054, pp. 31-42 : 37-39

Lithasia spicula sp. nov.

Sharp­tongued Rocksnail

Type Designations and Locality: Holotype NCSM 26807, Harpeth River, Highway 100 bridge, near Bellevue, Davidson County, Tennessee, U.S.A., 36º 03' 17" N, 86º 55' 43" W. Paratypes NCSM P4678, UAG 405.

Etymology: From Latin spiculum, a sharp point, referring to the pointed cusps on the lateral teeth.

Diagnosis: A species of Lithasia endemic to the Harpeth River in shoals under and immediately downstream of the Highway 100 bridge near Bellevue, Davidson County, Tennessee. The snail differs from other Leptoxis by having a shell morphology most like Li. armigera , from Lithasia by having three to four large, rounded denticles on the marginals, and from eastern North American pleurocerids by having pointed, triangular cusps on the lateral teeth.

Description: Shell to 35 mm long with 4­5 whorls, ovately conic, green­brown, with lateral brown­purple bands ( Figure 3 C). Sutures slightly impressed. Body whorl smooth, or with single row of small to well­developed tubercles; preceding whorls smooth or beaded in appearance near the suture. Aperture one­half shell length, fusiform, with a slight anterior channel. Posterior and anterior calluses on the columella absent. Radula rachidian wider than high, with nine pointed cusps, central cusp longest and broadest. Laterals with five to seven pointed cusps, central cusp longest and broadest. Outer marginals with three to four evenly sized, rounded denticles; inner marginals with eight to twelve evenly sized, blunt denticles.

Habitat and Distribution: The species is restricted to the shoals under and immediately downstream of the Highway 100 bridge. Individuals occur sympatrically with Le. praerosa on algae covered rocks and the gravel riverbed. No Lithasia have been found up to 100 m upstream of the bridge, and Li. spicula is replaced by Li. armigera further downstream.

Material Examined: Tennessee (all in Harpeth River): UMMZ 133988. Cheatham County — FLMNH 82103, near Shacklett; MCZ 93698, near Shacklett; UAG 555, Narrows of the Harpeth State Park; UMMZ 36451, Kingston Springs; UMMZ 53239, near Shacklett; UMMZ 53240, near Shacklett. Davidson County — ANSP 29294, near Bellevue; ANSP 69293, near Bellevue; ANSP 69333, near Bellevue; ANSP 176420, near Bellevue; FMNH 33656, near Bellevue; FLMNH 82068, below Bellevue; NCSM 26807, Highway 100, Bellevue; UAG 405, downstream of Highway 100 bridge, near Bellevue; UMMZ 36452, Bellevue; UMMZ 53232, below Bellevue; UMMZ 53233, below Bellevue.

Remarks: This species is tentatively placed in Lithasia based on conchological features. While data suggest it is not a Lithasia , it will most likely be identified as such in the field, and keeping it in Lithasia will allow future researchers and agencies to collect specimens accurately. Additional data is needed to determine the true generic placement of this unique pleurocerid.

It was thought that this population may be an example of an old, persistent, highly divergent haplotype of Li. armigera . Similar examples have been seen in Asian freshwater snails (D. O’ Foighil pers. comm.) and proposed in North American Elimia ( Dillon and Frankis 2004) , where rare, highly divergent haplotypes randomly appear at low frequencies in populations and form clades away from their cohorts. However, given the presence of a single haplotype in the Bellevue population taken from multiple individuals collected years apart and the unique radula structure, we believe it is more likely to be a new species.

Figures

FIGURE 3. Radulae and shells from Harpeth River pleurocerids. A. Li. armigera laterals from The Narrows of the Harpeth State Park. B. Laterals from “ Li. ” spicula, holotype NCSM 26807. Scale bars, 50 m. C. “ Li. ” spicula, holotype NCSM 26807, 31 mm.