Meiosis. But more specifically: Anaphase I.
A filter is a device that can reduce particulate in gaseous emissions from mobile exhausts. Specifically known as diesel particulate filter (DPF) removes soot from gasses of the diesel engine through the exhaust. It significantly reduces the amount of pollutants present in the air.
I think the hydra lacks the specialized cells for touch and chemical detection. On the other hand earthworms have touch, light, vibration and chemical receptors along the entire body surface. Both of them are invertebrates (those animals without a backbone), they include insects, worms, jelly fish, spiders among other animals.