Freshwater Mussels of Florida

Genus Utterbackia

Accounts for Genera and Species 360 Genus Utterbackia Baker 1927 Turgeon et al. (1998) recognized three species in Utterbackia. Utterbackia imbecillis is the most wide-ranging North American mussel species, occurring in Mississippi and Great Lakes basins, Gulf Coast basins from Mexico to Florida, and Atlantic Coast basins from Delaware to Florida. It has apparently been introduced in some Atlantic Coast rivers and peninsular Florida. Utterbackia is also known from early Pleistocene fossil deposits in the Leisey Shell Pits in the Tampa Bay area (Bogan and Portell 1995). type Species Anodonta imbecillis Say 1829 = Utterbackia imbecillis (Say 1829) Diagnosis Shell thin; smooth; inflated; outline oval to elliptical; umbo even with hinge line; umbo sculpture undulating, irregular ridges; periostracum shiny, occasionally dull, green to brown, with variable green rays; pseudocardinal and lateral teeth absent; nacre bluish white. Excurrent aperture smooth; mantle bridge separating excurrent and supra-anal apertures long; inner lamellae of inner gills connected to visceral mass only anteriorly; outer gills marsupial, with secondary water tubes when gravid; glochidia held across entire gill; marsupium thickened, not extended beyond original gill margin when gravid, marsupia creamy white when holding embryos, becoming rusty brown when brooding glochidia mature; glochidial outline subtriangular, with styliform hooks (Baker 1927, 1928; Britton and Fuller 1980). 361 Genus Utterbackia Utterbackia imbecillis (Say 1829) Paper Pondshell Utterbackia imbecillis – Upper image: length 84 mm, UF 47241. Apalachicola River below Jim Woodruff [Lock and] Dam at Chattahoochee, Gadsden County, Florida, 18 May 1974. © Richard T. Bryant. Middle image: length 58 mm, UF 449292. Flint Creek on U.S. Highway 301, about 4.4 miles northeast of junction of U.S. Highway 301 and State Highway 582, Hillsborough County, Florida, 20 May 2004. © Richard T. Bryant. Lower image: length 26 mm, UF 449292. Flint Creek on U.S. Highway 301, about 4.4 miles northeast of junction of U.S. Highway 301 and State Highway 582, Hillsborough County, Florida, 20 May 2004. © Richard T. Bryant. Description Size: length to 120 mm, in Florida to 102 mm. Shell: thin; smooth; small individuals compressed, large individuals inflated, width 25%–40% of length; outline oval to elliptical; anterior margin rounded; posterior margin narrowly rounded to bluntly pointed; dorsal margin straight, low dorsal wing typically present in small to medium individuals, usually absent in large individuals; ventral margin straight to broadly rounded; posterior ridge low, rounded; posterior slope moderately steep, flat to slightly concave; umbo broad, moderately inflated, typically even with hinge line, occasionally slightly above in large individuals; umbo sculpture undulating, irregular ridges (Figure 10.98); umbo cavity wide, shallow. teeth: pseudocardinal and lateral teeth absent. Nacre: white to bluish white, iridescent. Accounts for Genera and Species 362 Periostracum: shiny, occasionally dull to clothlike; small individuals yellowish tan or green to greenish brown, may be weakly rayed, large individuals dark olive brown, often obscuring rays. Figure 10.98. Umbo sculpture of Utterbackia imbecillis, length 22 mm, UF 455461. Peace River on County Route 640 bridge, about 5.5 air miles south-southeast of Bartow, Polk County, Florida, 24 May 2006. Illustration by Susan Trammell. Glochidium Description Outline subtriangular; length 248–313 µm; height 249–310 µm; width 148 µm; with styliform hooks (Ortmann 1912; Surber 1912; Hoggarth 1999; Schwartz and Dimock 2001) (Figure 10.99). Similar Sympatric Species Utterbackia imbecillis closely resembles Utterbackia peggyae and Utterbackia peninsularis but typically has a more elongate shell and is usually more pointed and narrow posteriorly. Utterbackia imbecillis typically has less prominent rays than U. peggyae and U. peninsularis. The mantle margin of live U. imbecillis is typically unpigmented, whereas those of U. peggyae and U. peninsularis have small dark spots, giving them a peppered appearance. Utterbackia imbecillis may resemble some Pyganodon grandis but differs in being more elongate and having a less inflated umbo that is even with the hinge line. Small Utterbackia imbecillis may resemble Anodonta couperiana, Anodonta hartfieldorum , Anodonta heardi, and Anodonta suborbiculata but lack the fine green rays on the umbo and upper portion of the shell disk, which are typically present in those species. Distribution in Florida Utterbackia imbecillis was historically distributed from Escambia to Apalachicola River basins. Its occurrence in the remainder of the state is the result of introductions and subsequent invasions (Figure 10.100). ecology and Biology Utterbackia imbecillis inhabits a wide variety of aquatic habitats including wetlands , marshes, swamps, creeks, rivers, ponds, and lakes. It also occurs in artificial habitats such as roadside ditches, canals, borrow pits...