I admit I had never given this question a lot of though before just recently. I am sitting through 7th grade classes learning what I didn't learn in my own middle school years and then some. I know what mycology, cytology and hystology are. I know what a chloroplast is and what it does.
And I know what defines animals as separate from plants. We watched a video about sea sponges this week. For a long time that bathroom scrubby was assumed to be a plant. Lately it has become apparent that it is actually an animal. It feeds itself rather than relying on photosynthesis, it reproduces via sperm and egg. But that is pretty much where the similarities to us stop.
Sponges are a collection of cells and spicules that make up the corrugated, folding, tubing forms you think of when you think sea sponge. Inside these forms are pockets, channels, chambers and flagellating 'hearts' that pump water through from the outside of the sponge to the inside hollow where the water is released back into the sea/ocean. The water carries micro organisms with it and they are filtered out and absorbed by the sponge as food.
The truly freaky thing about all this is that scientists are finding that these beauties are the oldest living common ancestor to the rest of us higher beings.
Gives 'sponge worthy' a whole new meaning!
Mom and Pop Sponge