The previous parts of this book use the general and informal term “testate rhizopods” to indicate both foraminifera and thecamoebians. Up to this point, however, the discussion has focused almost exclusively on foraminifera. This is because of the enormous body of information available on these organisms, which have been a key tool of micropaleontologists for either commercial or environmental applications for more than a century. Thecamoebians, on the other hand, have been the exclusive domain of geneticists, biologists, and taxonomists; no attempt has been made to use them as geological proxies until very recently. These organisms are not a familiar subject for most environmental managers. The literature concerning them is mainly in nongeological journals and is not always readily available. Although they inhabit mainly freshwater bodies, thecamoebian tests, either transported or indigenous, are also found in marginal marine environments. For these reasons, it was deemed appropriate for this book to summarize some of the relevant general information on these organisms in somewhat greater detail than was done for foraminifera.

THECAMOEBIANS

General Considerations

“Thecamoebians,” although morphologically similar and taxonomically close to foraminifera, are mainly freshwater organisms; very few forms tolerate mildly brackish conditions. The term “thecamoebians” (= amoebae with a test) is an informal one used to characterize a very diverse “group” of organisms belonging to two different classes within the subphylum Sarcodina (Fig. 1.1).