Hypotrichs possess compound ciliary organelles called "cirri," which are made up of thick tufts of cilia, sparsely distributed on the ventral surface of the cell.

The multiple fused cilia which form a cirrus function together as a unit, enabling the organism to crawl along solid substrates such as submerged debris or sediments.

[2][3][4] In older systems of classification, the term hypotrich comprised all ciliates possessing a relatively flattened body shape, strong cirri restricted to the ventral surface, and a large oral region (peristome) partially surrounded by an "adoral zone of membranelles".

[5] Any natural group, or clade, that contains both Euplotes and Oxytricha would also have to include many morphologically dissimilar spirotrich ciliates, such as the tintinnids and the oligotrichs.

[6] However, some prominent researchers—notably, the Austrian ciliatologist Helmut Berger—rejected Lynn's nomenclature, and continued to assign non-euplotid "hypotrich" ciliates, such as oxytrichids and urostyloids, to some variant of Friedrich von Stein's original order Hypotricha.