OK so we couldn’t resist sharing this colourful collage of Christmas Tree worms. It’s been done before but these critters never cease to amaze…
Spirobranchus giganteus is a tube-building polychaete that has a tubular, segmented body of an approximate length of 3.8cm covered with chaetae, small appendages that aid the worm’s mobility. Because it does not move outside its tube, this worm does not have any specialised appendages for movement or swimming.
The worms’ most distinct features are two “crowns” shaped like Christmas trees. These are highly modified prostomial palps, which are specialised mouth appendages. Each spiral is composed of feather-like tentacles called radioles, which are heavily ciliated and cause any prey trapped in them to be transported to the worm’s mouth. While they are primarily feeding structures, S. giganteus also uses its radioles for respiration; hence, the structures commonly are called “gills”.
One major difference between Christmas tree worms and other Sabellida fan worms is that the latter do not have any specialised body structures to plug their tube holes when they withdraw into them. S. giganteus, like other members of its family, possesses a modified radiole, usually called the operculum, that it uses to secure its hole when withdrawn into its tube.
This collection appears to be growing in a colony of green Porites coral.