'Ordered'and'unordered chevron structures'in serpulid tubes comprise minute calcite lath-like crystals. In ordered chevron structure (Pomatoceros triqueter) the crystals parallel each other within each chevron layer, whilst between layers the alignment direction alternates. The laths have no alignment in unordered chevron structure (Spirorbis and locally in Pomatoceros triqueter). In 'homogeneous chevron structure' (found in Jurassic pomatocerids) the layers comprise a granular or homogeneous fabric. This structure possibly represents a diagenetic replacement of lath-like crystals. Serpulid chevron structures are quite dissimilar from any shell microstructures described in molluscs or lophophorates. The secretion of microstructures comprising lath-like crystals may have allowed rapid tube growth. Spherulitic prismatic structure is identified in Spirorbis; the structure occurs locally in the outer part of the tube. The microstructure of Recent spirorbids is quite dissimilar to that of Palaeozoic fossils (microconchids) previously assigned to the genus Spirorbis.

Key words: serpulids, microstructure, biomineralization, ordered chevron structure, unordered chevron structure, homogeneous chevron structure, spherulitic prismatic structure.