The nautili are a successful family of widespread nautilidan cephalopod mollusks from the Late Triassic-Holocene of the entire world. They were named in 1825 by Henri Marie Ducrotay de Blainville. They are one of the few animals to be called "living fossils" (due to surviving up until now), and are the closest living relatives of Paleozoic cephalopods such as Cameroceras.
Nautili are unique mollusks. They are mainly squid-like in body plan, with a soft body, a mass of tentacles in the front of their body, large eyes, and a small, keratinous beak hiding in their of tentacles; however, they have 90 small tentacles instead of 8 long ones, large "pinhole" eyes, and a large, curly shell. Their bodies are covered in smooth skin, and mostly covered by their hard shells.
Nautili are predators, feeding mainly on fish and small crustaceans, but also scavenging carcasses. Their tentacles are used to get a hold of struggling prey, while their beaks are used to crush them and tear them into pieces.
The shells of nautili would serve three purposes: protection from predators (the cephalopods would hide in their shells when threatened), stabilization, and buoyancy control. In order to swim, they would pull water into their mantle before propelling themselves forward with a jet of water pushed out from the siphon; this causes them to swim with a seesaw-like motion. Unlike other cephalopods, who have eyes with large lenses, nautili have eyes with small, pinhole-esque lenses, which would have only detected simple images; due to this, they would have detected prey using their sense of smell. As well as this, they are nocturnal, and sink to the seafloor in order to rest during the day; it is only at night that they rise from the depths in order to forage and find mates.