External Morphology

The generalized body plan of the family Serpulidae is shown below:

The Christmas tree worm’s prostomium is only part of the worm directly exposed to its environment. It consists of two tentacles in the form of whorls with the top opening of each functioning as the mouth. The number of whorls present varies from 5 to 12, depending on the species. These whorls possess bipinnate tentacles called radioles. Attached to these radioles are many laterofrontal cilia called pinnules (Rupert E. E. 2004). These radioles and pinnules are spaced so that there are no conspicuous gaps in between them which would reduce their filtering efficiency. With beating motions of the pinnules towards the radioles, a current that allows the polychaete worm to suspension feed  from the water column is created (Strathmann, Cameron et al. 1984). The radioles and pinnules gather particulate matter from the nearby water column and transport it to the mouth along a groove inside the whorl lined with cilia. The whorls also have a respiratory function, with the current providing the means for this process to occur.  When the worm wishes to retract into the calcareous tube, it folds or rolls the radioles inside (Rupert E. E. 2004). Most species possess an operculum - a flap the size of the diameter of the opening of the calcareous tube – in between the whorls that protects the worm when the tentacles are retracted.

The majority of the worm resides within a calcareous tube for its entire adult lifespan. The worm is segmented with parapodia attached to each segment. This allows for attachment and unidirectional movement within the tube. The main body secretes a mucus within the tube in order to aid smooth movement.