Cephalopod ink is a dark-colored ink (dark-brown, or black, or violet-black) released into the water by most species of cephalopod, as an escape mechanism, from their ink sacs.
For human consumption, the ink is extracted during the preparation of the dead cephalopod (usually cuttlefish), from their ink sacs, and therefore contains no mucus.
Cuttlefish Ink, also known as 'Nero di Sepia', is primarily used as a food coloring and flavoring, especially in Japan and the Mediterranean, mostly in pasta, risotto and sauces, and of course the famous 'calamares en su tinta'.
Cuttlefish ink is a natural, organic, animal food colorant (black color).
Cephalopod ink is extracted from either squid, octopuses, or cuttlefish, but where squid ink is more purple and less viscous, a cuttlefish's is jet-black and jellylike with a reflective sheen, while taste-wise it has a briny, subtle oceanic salinity.
References: Read more about Cephalopod Ink on Wikipedia