An overview of the tube fabric of Pomatoceros (Polychaeta, Serpulidae), illustrated by examples from the British Isles

The calcareous tube of Pomatoceros is one of the most highly studied serpulid dwelling tube-structures. Despite this, there is a lack of consensus regarding the number and types of fabric within the tube structure, and the three-dimensional distribution of the fabrics about the tube. These are here described in Pomatoceros triqueter within the coastal waters of Britain, with lamello-fibrillar, irregularly oriented prismatic and spherulitic-prismatic fabrics noted as the major ultrastructural components. Fabrics are distributed along a chevron-shaped growth lamella structure, passing progressively from lamello-fibrillar fabric on the inner part of the tube, to irregularly oriented prismatic fabric along the outer part. This model can be adequately applied to all previous descriptions of the ultrastructure of Pomatoceros. All analysed samples comprise Mg-calcite, with typically 10-15 mol% MgCO3.