Squid sucker teeth and cocoons of a terrestrial flatworm: amino acid content of two nano-structurally identical tissues in phylogenetically unrelated taxa

Abstract

An extraordinary micro-structural similarity between squid sucker teeth and the egg shell of a terrestrial planarian worm has been reported, but to date only the amino acid content of the squid sucker tooth has been available. This prompted us to analyse the amino acid content of the planarian egg shell. Although both share an absence of detectable chitin and metal ions and both possess relatively high amounts of the amino acids GLY and HIS, the planarian egg shell is considerably richer in GLU, LYS and ASP. Most dramatic was the difference in TYR, which was the second most abundant amino acid in the squid, but hardly featured at all in the planarian egg shell. In the light of these new findings the different functional roles that the structures in question play in the lives of the two taxa are discussed. An EDS-analysis revealed clear C, N, and O peaks and additional very small peaks less than 0.1w% suggesting the presence of one or both S and Cl.

Keywords: amino acid composition; fibre proteins; nanotubes; terrestrial planarian egg shell.