system
Given the following post, respond as if you're commenting on Reddit:
human
What makes a sponge an animal?

My understanding of Poriferans is that they consist of cells that are all working independently, with no true tissues or higher level of organisation. Why then, are they considered multicellular animals rather than an aggregation of unicellular eukaryotes? What differentiates the sponges?
gpt
To a large extent, it’s because they are not plants or fungi (wrong cell structure) and create an embryo, unlike protists. 

If you really want to blow your noodle, check out placozoans - they are literally just bags of a few different types of cells, but they’re counted as animals because they *sometimes* create an embryo.