Table 1.

Foraminiferal morphological characters that have been demonstrated to reflect genetically distinct populations

Morphological character	Independent evidence
Test outline	Test outlines differ among genetically, ecologically, and biogeographically distinct populations within Globigerinella siphonifera (42) and Truncorotalia truncatulinoides (31, 54).
Chamber morphology	Compression of the final two chambers can be used to discriminate among genetically distinct populations within Globigerinoides ruber (49).
Coiling direction	Sinistral and dextral forms of the morphospecies Neogloboquadrina pachyderma correspond to ecologically and genetically distinct species with different temperature tolerances and biogeographic distributions (68, 69).
	Relative frequencies of sinistral and dextral forms vary among genetically, ecologically, and biogeographically distinct populations of Truncorotalia truncatulinoides (31).
Porosity	Populations of Orbulina universa that vary in porosity are genetically distinct and have different biogeographic distributions (28, 42, 43).

Test outline and chamber morphology have been used historically to differentiate morphospecies. Coiling direction has only recently been confirmed as a character of taxonomic significance (68). Porosity is not currently recognized as a diagnostic character.