Also known as Fat Sea Pen, Hair Sea Pen, Obese Sea Finger, Octocoral, Sea Cactus, Sea Feather, Sea Finger, Sea Quill.
Found on soft mud and sandy bottoms, over harbours and lagoons often withdrawing into the substrate during the day if threatened.
They feed on plankton.
Length - 10cm
Depth - 2-20m
Sea pens have a large central axial polyp with an internal calcareous axis. Half of the sea pen is buried as an anchoring root, the upper half reaches into the water to feed on plankton.
Sea Pens are often home to commensal crustaceans.
A few sea pens are found in shallow waters, but most are found in deeper waters where they are less likely to be disturbed.
Many sea pens are colorful and capable of spectacular bioluminescent light displays in the dark when alarmed. Ref: https://en.wikipedia.org/wiki/Cavernularia_obesa