Christmas tree worms

Perfect miniature Christmas trees round off our choice of festive critters.

Find out more:

Does Spirobranchus giganteus protect host Porites from predation by Acanthaster planci: predator pressure as a mechanism of coevolution (PDF)

Helen - Well, that brings us to our twelfth and final critter of Christmas. And how could I resist finishing with another group of great festive beasties - the Christmas tree Worm.

These critters really do look like titchy, one-inch Christmas trees and they've been one of my favourites for ages - you might have spotted them while scuba diving or snorkelling on a coral reef with their frilly crowns decorating boulders of live coral. 

They're a type of polychaete worm called a serpulid, and the bit you see sticking out is just their spiralling feathery head gear - a pair of appendages called radioles which they use to sift food and oxygen from the water.

The rest of their body stays safely inside a calcium carbonate tube inside the living coral - when they sense movement around them they quickly flip their radioles back in, and shut the tube tightly shut with another specially adapted radiole called an operculum.

There are two subspecies of Christmas tree worm, one from the indo-pacific and other from the atlantic and the Caribbean, and they come in all sorts of colours morphs - blue, red, orange, yellow, but the most common is white - appropriately enough for a snowy, seasonal critter.

As well as looking pretty, one study has suggested that Christmas tree worms play an important role in coral reefs by protecting living corals from attacks by crown-of-thorns starfish, which don't like being tickled on their sensitive undersides.

And apparently, they can live for up to 40 years. Not bad for a little worm.