Green Sea Pansy, Udotea flabellum, is a somewhat common algae found throughout the Caribbean and Western tropical Atlantic. They are found primarily in shallow waters, but can occasionally be found as deep as 50' or more. They will thrive in your reef tank or refugium and may go through die off and regrowth cycles. Each growth cycle can last for several months, and after they die off, the holdfast will send out a new shoot that will become a new "fan". The "fan" is calcareous and is dark green.