The trophozoites of Opalinaspp. are large, up to 1 mm in length, and live in the intestine of frogs. Although ciliated, these parasites are not classified with the Ciliata because the latter have nuclei of two distinctive sizes.
This photo shows the elongated teardrop shape of the body, which is covered in long cilia. Internally, the hundred of small dots are all nuclei. On close examination, although not evident in this photo, the nuclei are all similar in size.