Tubbs Blue
A variant of Zoanthids (Zoanthus sp.)

Representative Zoanthidsphoto — a dedicated image of this exact morph isn't available yet.
A blue-bodied Zoanthus (often listed as Zoanthus danae) prized for its intense blue-violet oral disc encircled by reddish-brown tentacles. One of the older, most recognizable blue morphs.
📜 Backstory
Tubbs Blue has been in hobby release since around 2002 and is sold by The Reef Farm, World Wide Corals, Vivid Aquariums, and others. Vendor lore (e.g. The Reef Farm) describes it arriving as a hitchhiker on a friend's Acropora colony; the named individual is informal and the broader lineage is origin debated, but the 2002 release is widely cited.
Keeper tips for this variant
Blue coloration holds best under bluer/actinic-leaning light; moderate flow and a mid-tank placement suit it well.