Pharaoh cuttlefish are cephalopods related to cuttlefish, squid, octopus and chambered nautilus. They have eight short arms and two long tentacles that are usually tucked neatly into their arms. The tentacles are deployed to catch prey. The cuttlefish's flat body allows it to live and hover near the ocean bottom where it finds its favorite food. An outer shell once covered the cuttlefish's body but has since evolved into a porous internal shell called a cuttlebone. The cuttlefish varies its buoyancy by varying the amount gas and liquid held in the holes of the shell.
A cuttlefish moves by undulating a delicate fringe that runs along its entire body, but for a quick getaway it expels a forceful stream of water through its siphon. When threatened, cuttlefish can produce a covering cloud of ink called sepia. Long ago, this dark-brown ink was used for writing and drawing.
Sharks, rays, dolphins sea birds and larger fish prey on cuttlefish. As with other sea life, overfishing and pollution are serious threats.
Males fight for choice mating dens. Most fights end without major injuries. After the males win their territory, female cuttlefish appear at the dens and mate with resident males. Fertilization is internal. Face to face the cuttlefish embrace and the male uses a special arm to transfer a sperm packet into the female's mantle cavity. After mating, the female retreats deep within the den where she lays her eggs one at a time. She coats the eggs with a protective sheath and carefully cements them to the roof of the den. She leaves the eggs unattended to develop and to hatch on their own. The female dies shortly thereafter.
Like their fellow cephalopods, pharaoh cuttlefish are master color changers. Known for their bright coloration and iridescent blue bands that run along the fringe of their mantle, they can rapidly change to ornate colors including metallic blues, greens golds and silvers. They also create skin patterns such as stripes, and spots. Cuttlefish and other cephalopods use color to communicate warnings, mood changes, courtship displays or for camouflage.
Cuttlebone is composed of calcium. This calcareous cuttlebone is often fed to birds to whet their beaks or as calcium supplements.