Vorticella and we already know, is single celled - a unicellular organism. It's tempting to think that anything that tiny must be single celled or at least, very simple. But that's not how it works, rotifers are real animals - multicellular creatures with nervous systems and everything, they're just a little on the small side.
Rotifers are a bit on the speedy side when you're steering a microscope by hand but with a bit of practise I managed to get some pictures.
A tiny bit of fern leaf here is like a whale carcass in the ocean depths - it's a massive pile of food that attracts animals from miles ( well, millimetres ) around.
Check this one out! Those oval things in the background are paramecium - single cells, you might just pick up the halo of cilia around them that they use to swim. Cilia are popular with small things. Our rotifer - an animal remember is not much bigger than them. You can see how it grips onto the substrate using a three toes foot and grazes bacteria and bits of plant from the surface. It even has a shell - a lorica - to give it some protection. It looks a lot like a shrimp - but it's not.
Rotifers have about a thousand cells, all rotifers of the same species have exactly the same number of cells and more than that - they're born with all the cells they will ever have, when they grow, their cells just get bigger. It's called eutely and a lot of tiny animals do it - you can grow a lot faster if you're not going to all the bother of copying all your DNA and making more cells. The downside is rotfiers don't heal if they get injured - they can't make more cells to patch up a hole so the slightest injury and it's curtains.
Here's another type - filter feeding. The cilia around the mouth are much more obvious. As this one looks like it's quite settled I can spend a bit of time using the bigger lenses to have a good look.