Christmas Tree Worm in Cozumel

Pairs of tiny spiral cones in vivid blue, orange, yellow, red or white, growing straight out of a coral head. They vanish instantly when a shadow or a hand passes.

Quick ID

Where You Will See It In Cozumel

Christmas Tree Worm works the 6 to 98 foot band. On this island that means the sheltered west-coast reefs, and the shallow east-side entries when the sea is flat — these are the sites where the depth and the habitat line up for it.

Without a boat. It is worth looking for at El Mirador, El Presidente and Money Bar — all shore entries, so you dive them on your own schedule.

On an ordinary beginner boat dive. It should be within reach at El Cielo, La Francesa, Las Palmas, Molas Shallow and Palancar Gardens. No advanced certification needed.

Deeper, and on the walls. It is also plausible on C-53 Wreck, Cantarel (Eagle Ray Wall), Chun-Chacaab and Colombia Deep.

Conditions change the odds more than the site does — the current, the time of day and how much the group has already stirred up the sand. Ask your guide what they have been seeing that week.

Behaviour

The visible spirals are gills and feeding structures. The worm's body lives inside a calcium tube bored into living coral, and it seals the entrance with a plug when it retracts. Withdrawal is triggered by shadow and pressure change, which is why they close before you arrive.

Commonly Confused With

• Social feather duster — Feather dusters form clumps of soft feathery crowns on a single stalk, in sand or rubble, not spirals in coral.
• Small anemones — Anemones have loose tentacles and do not retract into a coral tube.

Diving Etiquette And Safety

Do not wave a hand at them to make them retract. Repeated retraction costs the animal feeding time, and the game is played by every diver on the reef.

Part of the Cozumel marine life guide · see Cozumel dive sites · plan your Cozumel dive trip

Photo: James Guttuso, Public domain, via Wikimedia Commons.