like others have mentioned it is mermaid's cup/wine glass and isn't usually consider invasive and is more of a rarer algae to see in the hobby recently
crazy.. i just had some caulerpa pop up in one of my tanks that hasn't had any algae added ever.. a few coral frags over the last month... with no visible algae... must of had some dormant spores or something. I have also had corals lost in fallen cracks and such that have hung on for years to make a comeback when i do some tank re-org...