Testate amoebae (thecamoebians, formally Testacea or Thecamoeba) are a polyphyletic group of ameboid protists characterized by the presence of a test. Testate amoebae mainly include the Euglyphida (Rhizaria: Cercozoa) and the Arcellinida (Amoebozoa), but also some minor groups like the Amphitremida (Stramenopiles: Labyrinthulomycetes), the Tectofilosida (Rhizaria), Cochliopodium and Trichosida (both in Amoebozoa).
Traditionally, those species that form large networks of anastomosing pseudopodia, despite of some of them having tests, are not counted amongst testate amoebae; this comprises genus Gromia and the Foraminifera (both in Rhizaria).
The Thecamoebida (Amoebozoa), with the genus Thecamoeba, despite their name, do not have tests.
Testate amoebae taxa are differentiated by their test characteristics and the type of pseudopodia (lobose, recticulose, or filose). Arcellinid testate amoebae produce lobose (wide) pseudopodia while euglyphid testate amoebae produce filose (slender) pseudopods.
Testate amoebae are closely related to the Foraminifera.