The Argonaut or the Paper Nautilus.

baby-nautilus-in-shell-fbAmongst tidal debris there sometimes appears a thin papery shell, bearing on its white surface a ribbed pattern like that which shore currents impress upon sand. It is the shell of the paper nautilus or Argonaut, an animal distantly related to an octopus and like it , having eight arms.

The Argonaut lives on the high seas, in both Atlantic and Pacific Oceans. The “shell”is actually an elaborate egg case or cradle secreted by the female for protection of her young.
It is a separate structure that she can enter or leave at will.

The much smaller male ( about a tenth of the size of his mate) secretes no shell. He inseminates the female in the strange manner of some other cephalopods: one of his arms breaks off and enters the mantle cavity of the female, carrying a load of spermatophores.

The Argonaut is not the chambered or pearly nautilus of Holmes’s famous poem

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