Granulometric evolution of the sand tube in relation to growth of the polychaete AnnelidSabellaria alveolata(Linné) (Sabellariidae)

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Abstract
Earlier studies on the sedentary polychaete Sabellaria alveolata (Linné) (Sabellariidae) have revealed that the closely apposed neuropodia of setiger 1 function as a building organ that plays a fundamental role in constructing the tube. The present study investigated whether selection or calibration of sand grains is carried out by this organ. An analysis of worms of different sizes has shown that the height of the building organ increases in a predictable manner according to a well defined law as the animal grows. Granulometric studies of small portions of the tubes show that there is a relationship between the diameter of the sand grains and the height of the building organ. The increase in size (and thus also height) of the building organ is quite rapid during the first three years of the worms life and slows down thereafter. These results are statistically significant for isolated tubes but cannot at present be extended to blocks of tubes from the reef. Two possible explanations for this are, first, the rather small number of specimens (14) which have been examined, and second, and more important, the passive trapping of sediment between the tubes.