Wikipedia
The tectofilosids or amphitremids are a group of filose amoebae with shells. These are composed of organic materials and sometimes collected debris, in contrast to the euglyphids, which produce shells from siliceous scales. The shell usually has a single opening, but in Amphitrema and a few other genera it has two on opposite ends. The cell itself occupies most of the shell. They are most often found on marsh plants such as Sphagnum.
This group was previously classified as the Gromiida or Gromiina. However, molecular studies separate Gromia from the others, which must therefore be renamed. They are placed among the Cercozoa, and presumably developed from flagellates like Cryothecomonas, which has a similar test. However, only a few have been studied in detail, so their relationships and monophyly are not yet certain.