Ok I know its still April but that means there's only a coupla hundred shopping days til Christmas so I thought I should put up some Christmas trees. These are Christmas tree worms - so named for obvious reasons but known to scientists as Spirobranchus giganteus.
They tend to form colonies in boulder-style stony corals such as Porites, star and brain corals. The "christmas trees" themselves are the feeding apparatus that trap microscopic foods, the worm itself is below in its tube. The Christmas trees come in pretty much every colour imaginable (don't believe me? check this digitaldiver.net thread out). It s a pretty remarkable sight when you see a lump of boulder coral with a dozen or so worms in 3 or 4 bright colours poking out.
The one thing I'm not such a big fan about with these worms is that they are photosensitive and react to sudden changes in light levels (such as a photographer hovering 3 inches away) by withdrawing into their tubes. So just as you get a particularly nice coloured worm in your sights (my favourite was a primrose yellow one on a cambridge blue staghorn coral) and nicely composed when the worm disappears. They come back out after a little while but when diving its not always practical to wait and there's no guarantee you won't make the same mistake again.
For the sake of precision the top two are the subspecies S. giganteus giganteus and the bottom one is S. giganteus corniculatus. How can I tell? Easy because I know where the pictures were taken; the top 2 are Carribean specimens and the bottom one is from the Red Sea