Aiptasia anemone, also known as Glass anemone are a major pest in the reef tank community. There are several ways to eradicate them, such as hitting them with lime water or introducing predators like peppermint shrimp and foxface fish.
This is more like what an every-day aiptasia sighting is like.
This is an amazing photo of an Aiptasia. This is exactly what every aiptasia that I've ever seen looks like.
This video has someone demonstrating how to get rid of an Aiptasia anemone with Aiptasia X (aka concentrated limewater).
I've never seen a syringe needle used first. I've always gone for the big gun, which can result in the anemone getting spooked too early. The needle on the syringe probably allows for a sneakier attack.