The chitin from pogonophore tubes is shown to be essentially the same as that from the pen of the squid Loligo and is classified as β-chitin (as are the known chitins in annelids). However, certain important differences in detail are seen when comparing X-ray diffraction photographs and infra-red absorption spectra of the chitin from the two sources. These matters are of interest in defining the systematic position of the Pogonophora as well as in reaching an understanding of the functions of the protective tube.