Freshwater Mussels of Florida

Genus Glebula

237 Genus Glebula Genus Glebula Conrad 1853 Glebula is monotypic (Turgeon et al. 1998). It occurs in Gulf Coast basins from Texas to the Florida panhandle. It is also found sporadically in Arkansas and eastern Oklahoma and historically in the Ohio River (Watters et al. 2009). Glebula rotundata is somewhat unusual in that it typically occurs in the extreme lower reaches of coastal rivers in areas that may occasionally experience intrusion of brackish water. Glebula rotundata is likely the most euryhaline species of mussel in Florida. In a controlled laboratory experiment, G. rotundata was able to survive at least 24 days in salinities up to 12 ppt (Johnson et al. in review). type Species Unio rotundatus Lamarck 1819 = Glebula rotundata (Lamarck 1819) Diagnosis Shell moderately thick; smooth; outline elliptical; female shells swollen posterioventrally ; posterior ridge low; periostracum clothlike to dull; umbo moderately to highly inflated; pseudocardinal teeth divided into small, radially arranged serrate ridges, 2 in left valve, 1 in right valve; lateral teeth thin to moderately thick, 2 in left valve, 1 in right valve. Inner lamellae of inner gills completely connected to visceral mass; posterior half of outer gills marsupial; glochidia held in posterior portion of gill; marsupium extended beyond original gill margin when gravid; glochidial outline subelliptical, without styliform hooks (Conrad 1853; Simpson 1900a, 1914). Accounts for Genera and Species 238 Glebula rotundata (Lamarck 1819) Round Pearlshell Glebula rotundata – Upper image: female, length 103 mm, UF 375985. Slough off Tensaw Lake, 1 air mile southwest of Hubbard Fish Camp and Landing, Baldwin County, Alabama, 18 September 1999. © Richard T. Bryant. Middle image: male, length 77 mm, UF 375985. Slough off Tensaw Lake, 1 air mile southwest of Hubbard Fish Camp and Landing, Baldwin County, Alabama, 18 September 1999. © Richard T. Bryant. Lower image: length 39 mm, UF 449288. Apalachicola River at river mile 46.8, Gulf County, Florida, 7 August 2006. © Richard T. Bryant. Description Size: length to 150 mm, in Florida to 96 mm. Shell:smallindividualsthin,largeindividualsmoderatelythick;smooth;moderately to highly inflated, width 30%–60% of length, small individuals more compressed; outline oval to round; anterior margin rounded; posterior margin rounded to obliquely truncate; dorsal margin straight in small individuals, rounded in large individuals; ventral margin broadly rounded; sexual dimorphism subtle, females swollen posteriorly, slightly less 239 Genus Glebula elongate than males; posterior ridge rounded to weakly angular; posterior slope steep, slightly concave to slightly convex; umbo broad, inflated, even with hinge line in small individuals, elevated slightly above in large individuals; umbo sculpture thin, irregular ridges; umbo cavity wide, shallow to moderately deep. teeth: pseudocardinal teeth moderately thick, with radially arranged serrate ridges, 2 teeth in left valve, 1 tooth in right valve, small individuals with 2 thin, bladelike teeth in each valve; lateral teeth short, thick, straight to slightly curved, 2 in left valve, 1 in right valve; interdentum long, narrow. Nacre: white, pinkish, or purplish. Periostracum: typically clothlike; small individuals tan to brown, underlying purple nacre may give pinkish cast, occasionally with rays, large individuals usually dark brown to black. Glochidium Description Outline subelliptical; length 169–188 µm; height 183–198 µm; width 113–118 µm; ventral margin with internal irregularly perpendicular rows of lanceolate micropoints (Figure 10.45). Similar Sympatric Species Glebula rotundata can be distinguished from all Florida mussels with which it cooccurs by its oval to round outline, umbo even with hinge line or elevated only slightly above, brown periostracum without rays, narrow interdentum, shallow umbo cavity, and unique pseudocardinal teeth that have numerous radially arranged serrate ridges. Distribution in Florida Glebula rotundata occurs in Escambia, Choctawhatchee, Apalachicola, and Ochlockonee River basins (Figure 10.46). ecology and Biology Glebula rotundata occurs in large creeks to rivers, sloughs, and floodplain lakes. It occurs in moderate to no current in substrates of silt, mud, and sand, often with detritus. It is tolerant of brackish water and co-occurs with euryhaline bivalves such as Mytilopsis leucophaeata and Rangia cuneata. Glebula rotundata has generally been considered to be a long-term brooder, overwintering their larvae and releasing them with increasing temperature. However, brooding period of G. rotundata appears to be atypical from those of other long-term brooders or at least exhibits regional differences. In Louisiana it was reported to be gravid from March to early October (Parker et al. 1984). In Florida, populations in Apalachicola River were gravid from June to August (Brim Box and Williams 2000) and in Escambia River...