July 30. Christmas Tree Worms on Brain Coral while diving in Isla Mujeres Mexico.
The worms' most distinct features are two "crowns" shaped like Christmas trees. These are highly modified prostomial palps, which are specialized 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, they also uses its radioles for respiration; hence, the structures commonly are called "gills." Because it does not move outside its tube, this worm does not have any specialized appendages for movement or swimming. If you get too close, they completely disappear, they retract very quickly back into their tube.