Note 53 — Chapter VIII · THE BUILDING OF REEFS

These tubes form a mass by coiling loosely together like a cluster of worms, though the animal which makes them is exactly like those that have regular spiral shells and move about freely, e.g. the whelks. The young Vermetus has a shell like a young whelk, but as it then fixes itself down, the shell degenerates, and grows into the loosely coiled tube of the adult mollusc. Nothing could be more different than the body of a Vermetus and that of a worm, the resemblances between the shell of the one and the tube of the other being pure coincidence.