They are closely related to the Imbricatea, a group of testate amoebae with tests composed of inorganic silica scales.

They ancestrally glide on their posterior flagellum only and have a benthic distribution, but many lineages have evolved as planktonic swimmers, like the Ebriacea which have lost their pseudopodia.

It belongs to the subphylum Monadofilosa, a group of cercozoan classes that evolved after the early divergence of Reticulofilosa.

Thecofilosea is the only group of testate cercozoan amoebae with ancestrally organic scale-lacking shells, while all the Imbricatea (to which the scale-bearing Kraken belongs) have non-organic silica scaled tests.

They were first described as uninucleate cells surrounded by an organic flexible tectum (in the case of Tectofilosida) or a rigid test (in Cryomonadida) with one or two apertures for filopodia, either two flagella or none, and tubular mitochondrial cristae.