"Otters have a skin flap that forms a pocket so they can keep their favorite rock with them. They use this rock to break open mollusks when eating. Some otters go their entire lives carrying the same rock!” source
This is actually a test showing how sponges pump water through themselves for filter feeding!
They simply colored the water around them so you could easily see the process.
I’m very very late ! ê___ê’
Here some pics of my children book”The little Red Wolf” ! :>
Now available in french bookstore and on amazon !
(Pretty photos of the book by Jonathan Garnier : http://a-lifi.tumblr.com/ )