Chapter 20 

 Order 4 Testacea Schultze 



THE Testacea or Thecamoeba comprise those amoeboid organ- 

 isms which are enveloped by a simple shell or test, within which 

 the body can be completely withdrawn. The shell has usually a single 

 aperture through which pseudopodia protrude, and varies in shape 

 and structure, although a chitinous or pseudochitinous membrane 

 forms the basis of all. It may be thickened, as in Arcella and others, 

 or composed of foreign bodies cemented together as in Difflugia, 

 while in Euglypha siliceous platelets or scales are formed in the 

 endoplasm and deposited in the shell. 



The cytoplasm is ordinarily differentiated into the ectoplasm and 

 endoplasm. The ectoplasm is conspicuously observable at the aper- 

 ture of the shell where filopodia or slender ectoplasmic lobopodia 

 are produced. The endoplasm is granulated or vacuolated and con- 

 tains food vacuoles, contractile vacuoles and nuclei. In some forms 

 there are present regularly in the cytoplasm numerous basophilic 

 granules which are known as 'chromidia' (p. 44). 



Asexual reproduction is either by longitudinal fission in the forms 

 with thin tests, or by transverse division or budding, while in others 

 multiple division occurs. Encystment is common. Sexual reproduc- 

 tion by amoeboid or flagellate gametes has been reported in some 

 species. 



The testaceans are mostly inhabitants of fresh water, but some 

 live in salt water and others are semi-terrestrial, being found in 

 moss or moist soil, especially peaty soil. Biology of soil-inhabiting 

 forms (Volz, 1929); ecology (Hoogenraad, 1935). 



Shell simple and membranous 



Filopodia, in some anastomosing Family 1 Gromiidae 



Pseudopodia fllose, simply branched Family 2 Arcellidae (p. 476) 



Shell with foreign bodies, platelets, or scales 



With foreign bodies Family 3 Difflugiidae (p. 482) 



With platelets or scales Family 4 Euglyphidae (p. 487) 



Family 1 Gromiidae Eimer and Fickert 



These forms are frequently included in the Foraminifera by other 

 authors. 



Genus Gromia Dujardin (Allogromia, Rhynchogromia, Diplo- 

 gromia Rhumbler). Thin test rigid or flexible, smooth or slightly 

 coated with foreign bodies; spherical to elongate ellipsoid; aperture 



472 



