Dear all, 3rd part of our serial about spirorbin tubes ultrastructues is published ( Ippolitov, Rzhavsky 2015. T ube morphology, ultrastructures and mineralogy in recent Spirorbinae (Annelida: Polychaeta: Serpulidae). III. Tribe Circeini You can download it free here http://kmkjournals.com/upload/PDF/IZ/IZ%20Vol%2012/invert12_2_151_173_Ippolitov_Rzhavsky_for_Inet.pdf -- Alexander Rzhavsky