Freshwater Mussels of Florida

Key to the Additional Bivalves in Inland Waters

Additional Bivalves in Inland Waters 416 Sphaerium striatinum (Lamarck 1818) Striated Fingernailclam Description Length to 15 mm; shell rectangular; umbo central to anterior, low, extending slightly above shell margin; dorsal margin slightly to strongly convex; ventral margin broadly rounded, joining anterior and posterior ends with rounded angles; height/length ratio ~0.79; width/length ratio range 0.56–0.68; periostracum dull, striae variable in coarseness , irregularly spaced, often prominent over entire shell (Mackie 2007). Range Sphaerium striatinum is the most common and widespread species of Sphaerium in North America (Mackie 2007). In Florida it occurs in St. Marks, Aucilla, and Suwannee Rivers (Heard 1979a). Remarks Sphaerium striatinum occurs in creeks, rivers, and lakes but is rare in ponds and swamps with stagnant water (Herrington 1962; Heard 1979a; Mackie 2007). Sphaerium striatinum inhabits substrates of mud, sand, gravel, and rubble (Mackie 2007). Key to the Additional Bivalves in Inland Waters Using a key to identify bivalves can be challenging. Identifications of three of the families—Dreissenidae, Mactridae, and Cyrenidae—included in the key are relatively easy to distinguish based on their distinctive shell characteristics. However, the fourth family, Sphaeriidae, can be very difficult to identify. Additional references may be needed to distinguish some species of this family (e.g., Heard 1979a, Mackie 2007). The following key to the additional bivalves in Florida’s inland waters is in the standard dichotomous format. Each numbered couplet provides a contrasting set of characteristics which leads to the identification of a particular taxa or to an additional couplet. The number in parentheses indicates the couplet that led to it. This allows the user to work backwards through the key to check a questionable identification. 1 Umbo terminal or subterminal; shell byssate ............ family Dreissenidae, 2 Umbo central or subcentral; byssal threads absent on living specimens ......5 2(1) Internal shell with apophysis anteriorly near septum.......genus Mytilopsis, 3 Apophysis absent from anterior region of shell...............genus Dreissena, 4 3(2) Shell elongated, height/width ratio 1.30; apophysis pointed, often hook-shaped (may be found in inland waters) ........................................................ Mytilopsis sallei Additional Bivalves in Inland Waters 417 4(2) Venter of each valve with a sharply acute angle, resulting in the concave appearance of the ventral aspect of the shell (not presently known from open waters of Florida)....................................................... Dreissena polymorpha Venter of each valve with rounded obtuse angle, resulting in the convex appearance of the ventral aspect of the shell (not presently known from open waters of Florida).............................................................Dreissena bugensis 5(1) Hinge internal, chondrophore between cardinal and posterior lateral teeth; shell thick, heavy......................................family Mactridae, Rangia cuneata Hinge external, without chondrophore; shell variable, not thick and heavy.6 6(5) Each valve with three distinct cardinal teeth on well-developed hinge plate . .........................................................................................family Cyrenidae, 7 Neither valve contain three distinct cardinal teeth....... family Sphaeriidae, 9 7(6) External shell with distinct, widely separated (>1 mm), concentric ridges; lateral teeth of internal shell serrated...............................Corbicula fluminea Concentric ridges absent from external shell; lateral teeth not serrated......... .......................................................................................genus Polymesoda, 8 8(7) Shell oval shaped; periostracum dark with wavy, scaly ridges; beaks usually eroded in adults........................................................Polymesoda caroliniana Shell wedge shaped, suboval; periostracum translucent; scalelike ridges absent ; beaks not eroded in adults (may be found in inland waters) .................. ......................................................................................Polymesoda maritima 9(6) Each valve with one cardinal tooth; shell mottled with dark color pattern..... .............................................................................................. Eupera cubensis At least one valve (usually right) with two cardinal teeth; shell not mottled.. 10 10(9) Umbos anterior, or if subcentral, located on anterior side of center...........11 Umbos posterior, or if subcentral, located on posterior side of center ........... ..........................................................................................genus Pisidium, 17 11(10) Valves calyculate..............................................genus Musculium, in part, 13 Valves not calyculate, although an annulus or rest mark may be present...12 12(11) Hinge plate between umbos narrow, less than or equal to the width of the thickened end of the single cardinal tooth in the right valve .......................... ..........................................................................genus Musculium, in part, 13 Additional Bivalves in Inland Waters 418 Hinge plate between umbos thick, greater than two times the width of the thickened end of the single cardinal tooth in the right valve .......................... .......................................................................................genus Sphaerium, 16 13(11,12) Shell long in outline, height/length ratio ≤0.75 ....... Musculium transversum Height/length ratio ≥0.80............................................................................14 14(13) Length of adult shell 8 mm; shell outline more symmetrical, ventral margin slopes only slightly upward.........................................................................15 15(14) Umbos pointed; posterior end forming obtuse angle with dorsal...