Scanning electron microscope observations on the tube of the reef-forming serpulid Ficopomatus enigmaticus (Fauvel) (Annelida, Polychaeta)

The tube of Ficopomatus enigmaticus (Fauvel) has two different layers: an outer, 90 mu m-thick calcareous one and an inner, very thin organic membrane. Prismatic crystals, about 5 mu m in length, are evident at the inner surface of the calcareous layer. In the reef-like aggregates, tubes grow perpendicular to the substratum and are closely packed: their density ranges from 70 000 to 180 000 worms . m(-2), and distance between tube mouths averages 1.2 mm. Adherence between tubes appears to be due to wedge-shaped junctions, consisting of 10-12 mu m-long clusters of crystals. Small tubes of newly settled individuals encrust interweaving adult tubes and help to consolidate the reef framework.