Sources : Conchis

Pliny the Elder [1st century CE] (Natural History, Book 9, 49): Mucianus has stated that he has also seen in the Dardanelles another creature resembling a ship under sail: it is a shell with a keel like a boat, and a curved stern and beaked bow. In this (he says) the nauphus, a creature like the cuttle-fish, secretes itself, merely by way of sharing the game. The manner in which this takes place is two-fold: in calm weather the carrier shell strikes the water by dipping its flappers like oars, but if the breezes invite, the same flappers are stretched out to serve as a rudder and the curves of the shells are spread to the breeze. The former creature delights (he continues) to carry and the latter to steer, and this pleasure penetrates two senseless things at once — unless perhaps human calamity forms part of the motive, for it is an established fact that this is a disastrous omen for mariners. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Fish 7.23): As Pliny says, shells (concha) in the sea are keeled after the manner of ships, the bows bent, the prows pointed. In this is kept the nauplius, which is a small cuttlefish-like animal, only for company to play with. And this wonder, that for this the shell opens its valves and admits the nauplius to play, well aware that it will not be deceived by fraud by the guest admitted. - [Badke translation/paraphrase]