Can someone explain what exactly Aiptasia are?
Aiptasia is actually a Genus. There are hundreds of different Aiptasia sub-species - thus the subtle differences in coloration, etc. They are known mostly for their ability to reproduce asexually, and quite rapidly.
The nematocysts of aiptasia have a toxin that is more potent than that of most corals maintained in captivity. If I remember right, the only coral that has a more potent sting than Aiptasia is the Elegance coral. This is primarily why Aiptasia are so hated - they can proliferate rapidly, and given their sting, they can potentially kill all other corals and quickly take over a reef tank.
The "Curlique Anemone" (Bartholomea annulata) is in the Aiptasiidae family.