The body of Siboglinidae or Beard Worms is divided into four main sections. The anterior region (the front end) which is often called the cephalic lobe and which supports the tentacles (these vary in number from 1 to more than 1,000). Behind this is the short 'Glandular Region'. It is this area which contains the cells that secrete the tube within which the animal lives. These tubes are composed of a mixture of proteins and chitin and are normally stand upright and are buried, to about 50% of their length in the substrate (sand or mud or fine gravel i.e. the sea floor). In many species the glandular region includes some ridges of thickened cuticle which are called the bridle and which help the animal hold itself steady in its tube. This bridle is sometimes referred to as a frenulum. In the Vestimentiferans it is replaced by two folds or flaps of cuticle which perform a similar role.
Behind the glandular region lies the trunk. This is by far longest body segment and it makes up most of the animals length. This trunk bears two rows of papillae (little bumps or warts) along its length and in many species there is a girdle, or belt, of toothed setae somewhere near the midpoint of the trunk. Like the 'bridle' these setae also help the animal hold its place within its tube. Finally the animal's body ends with a short opisthosoma of from 5 to 30 segments. This opisthosoma is thicker than the trunk section and is buried in the substrate beyond the end of the animals tube
|