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The belemnite (Acanthoteuthis marinus) is a species of small squid-like cephalopod part of the belemnite family that originally lived in the Late Jurassic seas as an extinct species of Acanthoteuthis and was once extinct, but has since been brought back from extinction by SciiFii and introduced throughout the modern world's oceans to help boost biodiversity. Uniquely among the cephalopods, the belemnite has an internal shell beneath its skin, which is powered by the animal's fins to help it swim. The belemnite primarily swims head down in a vertical orientation similarly to native modern cephalopods like Spirula and Mastigoteuthis. The belemnite prefers to inhabit the upper 200 meters of oceanic waters, and the belemnite has an ink sac for defense against any potential danger. Like several other cephalopods, the belemnites have planktonic forms that inhabit the epipelagic and upper mesopelagic zones. The conservation status of the belemnite is Least Concern due to successful conservation efforts, the belemnite's wide range and its tolerance to many of the human activities. The belemnite is also one of the economically important food sources for people due to an increasing demand for the belemnite's tentacles and eggs.