by Matthew Cobb
The title of this post – “How extremely stupid not to have thought of that!” – was Thomas Huxley’s response when reading Darwin’s idea of evolution by natural selection. It was also my response, and Jerry’s, on seeing this amazing video of sponges eating.
Every year, I teach students that sponges are animals, and that they eat by wafting water currents through their bodies, with a flagellum situated in structures called collar cells. The flagellum captures tiny organic particles in the water, which are then absorbed into the sponge’s body and used for both metabolism and to make more sponge. Whenever I’ve said this in a lecture, there’s been a tiny voice in my head saying ‘But how strong is that current? Can they really get enough particles to grow? Am I actually telling the truth?”.
Now I know the answer – the current creating by those hundreds of thousands of whipping flagella is amazingly strong, as shown by this simple experiment: you release a dye around a sponge, and see what happens to it. How extremely stupid of me not to have thought of that!