Christmas tree worm [97K]

The cone-like shape and magnificent twin spiral plumage of this serpulid tube-dwelling worm has earned the name "Christmas tree worm" among divers and aquarists. Among the sedentary polychaete worms, it is widely admired and easily spotted, though small (this one is less than 1 1/2 inches or 3.8 cm in span). The colorful tentacles are used for feeding on passing suspended particles and for respiration. Much of the worm is anchored in its burrow, a hole bored into a live calcareous coral. 

These worms are very sensitive to disturbances, and are therefore difficult to approach without at least one episode of a near-instant retraction into the burrow. Touching the tentacles, or even the passing of a shadow can cause a defensive reaction. Fortunately they don't stay hidden for too long, usually under a minute, before slowly emerging from the burrow to display the tentacles in their full glory. Though worth the effort to photograph, I found the most effective technique to involve prepositioning the camera near the worm's burrow and waiting for it to emerge, while controlling my breathing to avoid disturbances created by bubbles.

Identification:  Spirobranchus giganteus (Phylum Annelida, segmented worms)

related links: 

Annelid Resources web site
short sea worms description from Sea and Sky
Reefkeepers Guide to Invertebrate Zoology Part 9: Polychaetes
and Part 10, by Rob Toonen
essay "Porites and Christmas Tree Worms", article by Rob Toonen
Polychaete (aka "bristleworm") FAQ For Reefkeepers version 1.0 by Rob Toonen (part 2 is sedentary polychaetes)

another fine worm [113k]

different angle, in blue [122k]

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