As you crawl along, you sometimes stop and rear your little wormy head up into the passing water. A nice little plankton occasionally drifts into your mouth as a result. A bigger mouth develops, which makes this more likely, and the edges of the mouth become frilly with cilia edgings, which wave in passing food.
You crawl less and less, and while you rear up your head, you dig your tail down to help you stay anchored.
When you create eggs, your larvae are free swimming until they find a good place to live, at which point they start to change shape, and excrete a glue which helps them stay still. There you will stay for life, often in a small colony of similar, possibly even related, filter feeding worms called Pterobrachia.
Evolution starts with the Last Universal Ancestor.
You can find out what happened before evolution here.
You can also short-cut to Land plants, or Animals
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