Magnautilus

The magnautilus is a relatively abundant sea creature in places in the world where iron accumulates, such as oceanic wrecks and junkyards. They resemble the nautilus from which they get their name, but with shells made of dull reddish stone. The shell is a biological form of iron, and is notable for being much stronger than other nautilus shells, although prone to denting. They come in many sizes, ranging from 5 millimeters to 2 meters.
Magnautiloids take advantage of the magnetic material in their shells. All magnautiloids have tentacles with small, powerful biomagnetic tips, which they use to inscribe patterns of magnetism into their shells, communicating surprisingly complex messages; scholars sometimes refer to them as the "birdsong of magnetic fields". They can use their magnetic tentacles to read the patterns of nearby neighbors and, in what appear to be very aggressive attacks, vandalize each other's shells.
Magnautiloids can be farmed by submerging iron-rich material in the sea. Every part of the creature is usable: the meat is comparable to scallop, and considered a delicacy in many places; the shell is prized by smiths as a metallic material that is practically immune to the chemical ravages of seawater; and the strong biomagnets harvested from the tentacles are prized by both artificers and engineers.
Magnautiloid magnets revolutionized arcanotech in the early centuries of the Age of Ascendants. Previously, the most precise magnets available were weak, heavy lodestones. The discovery of magnautilus farming techniques drove up the availability of the magnets, which even have been seeing use in the arcane community, generating much excitement about the possibilities.
In more modern times, the creatures have been seeing extensive use in sanitation systems, where the filter feeding magnautiloids thrive in the nutrient rich environment of sewer systems, providing cheap waste management solutions. Most non-desperate people avoid harvesting from these particular populations, but the creatures reproduce quickly, so are often staple food source for the desperate and destitute.