Freshwater Molluscan Fauna 
113 
Changes in the Molluscan Fauna 
All of the species recorded during this survey are common natives 
and were probably present in the lake in prior years but were simply not 
mentioned in previously published accounts. 
Neither Planorbella magnifica nor Helisoma eucosmius has survived 
in Greenfield Lake, as Fuller (1977) conjectured. Until recently both of 
these species were considered extinct by some authors (Opler 1976, 
Imlay 1977, Palmer 1985), but P. magnifica has recently been found in 
Orton Pond, approximately 40 km S of Greenfield Lake (Adams and 
Gerberich 1988). Helisoma eucosmius has not been located at Orton 
Pond, but the habitat appears to be suitable for it. 
Campeloma geniculum was not positively identified from the lake. 
One specimen of what appeared to be this species was collected at 
Station 15, but owing to the difficulties associated with separating it 
from C. decisum and the fact that only one was encountered, the 
specimen was counted as C. decisum. 
Gillia altilus and members of the genera Amnicola and Laevapex 
were not found in this study. Suitable habitat for these species has 
probably been eliminated by changes in the lake. 
By comparing Tables 1 and 2, it can be seen that virtually all of the 
gastropods collected during this study represent new species records for 
the lake. Of the species represented in Table 2, only the identifications 
of the Physidae are uncertain. The species Physella hendersoni and P. 
heterostropha could be expected to occur in Greenfield Lake. These 
species are difficult to separate based on shell characters, and Burch 
(1982) provides only illustrations. Physella heterostropha tends to be 
more robust than P. hendersoni, and it was on this character that the 
species were separated. “Robustness,” however, is a very weak taxonomic 
character. 
Changes in the molluscan fauna of the lake are most dramatically 
shown in the virtual elimination of the Unionidae. Only two species, 
Anodonta cataracta (= A. teres ) and A. imbecillus, are found in the 
Greenfield Lake system today compared with 10 that were recorded 
historically. The loss of Anodonta couperiana from the lake, previously 
suspected by Shelley (1987), has been confirmed. Eupera cubensis, a 
sphaeriid also previously reported from the lake, could not be relocated. 
When the decline of the Unionidae began is impossible to place. 
However, since Bailey collected Elliptio fisheriana in 1940 and Morrison 
mentioned three species of Anodonta in the lake in 1972, it would 
appear that this is a recent and rapid phenomenon. 
The two brackish-water species, Rangia cuneata and Polymesoda 
caroliniana, and the freshwater sphaeriid, Sphaerium occidental , are 
the only new records of bivalves from the Greenfield Lake basin. 
