At work we somehow landed on the topic of how many holes a human has, which then evolved into a heated discussion on the classic question of how many holes does a straw have.
I think it’s two, but some people are convinced that it’s one, which I just don’t understand. What are your thoughts?
Flatworms have a single opening that leads to a branching cavity (an incomplete digestive system). This means that the single opening is for both ingesting nutrients and expelling waste. While your mouth may be attached to your anus via the alimentary canal, I think it beats the hell out of having one multi-purpose opening, imho.
Right, technically a human only has 1 hole for ingesting nutrients and expelling waste as well though, assuming you are talking about the mouth and anus. Does a flatworm have any other through holes though e.g. nostrils or tear ducts? I have no idea what the biology of a flatworm is haha.
No, gas exchange is by simple diffusion across the skin and gut. No ears or eyes per se, just some photosensitive cells in slight depressions on the head. Planaria are pretty simple as far as animals go.