It is, like other members of the genus, dorso-ventrally flattened and flexible. There is a flexible sleeve around the base of the anterior flagellum. This flagellum is about 0.5 times the length of the cell, and it is the same thickness as the posterior flagellum. The recurrent posterior flagellum is slightly longer than the cell and trails under the body, to which it attaches loosely in a slight groove. The nucleus is situated subapically near the right margin of the cell.
Some cells have granules alongside the recurrent flagellum.
The species is distinguished because it is bigger than the more common A. debruynei, because it has a longer anterior flagellum and because it may have ventral granules. Also, A. mutabilis overlaps with A. terricola in the appareance of the anterior flagllum. References Griessmann, K. 1913. Larsen, J. and Patterson, D. J. 1990. Lee, W. J. and Patterson, D. J. 2000.