Can animal cells be unicellular?

At school we learnt about unicellular organisms, as well as prokaryotic and eukaryotic cells. Our teacher mentioned that some eukaryotic cells could be unicellular organisms (eg. amoeba) and showed us some diagrams. However, I saw that one of those cells was distinctly an animal cell, as it had a cell membrane. Can animal cells be unicellular as well? I looked it up online but can't find any example of this (I only found protozoans, protists etc). Is there an exception to this or is the teacher wrong? Thanks for your help!

Hi Sarah,
Animals are multicellular by definition. All animals develop from a single cell (the zygote) and there are some animals that can reproduce or regenerate from a single cell, but they still must spend at least part of their life cycle in a multicellular state. All cells have a cell membrane so that would not be defining feature of animal cells. Some organisms have cells with an extra layer called a cell wall, but animal cells do not posess this feature.