Overview

The term "nautilus" refers to the shelled cephalopods of the family Nautilidae, members of the subclass Nautiloidea and part of the larger group of cephalopods. These animals are often called chambered nautiluses because their shells contain a series of gas-filled chambers that help control buoyancy. Many biologists describe nautiluses as "living fossils" because their overall body plan resembles forms known from deep time, and they are the only surviving relatives of a once-diverse lineage that produced groups such as the ammonites in the Palaeozoic and Mesozoic eras.

Physical characteristics

Nautiluses have a distinctive external, spirally coiled shell with internal septa dividing it into chambers. The soft body occupies the outermost chamber; as the animal grows it seals off earlier chambers and can adjust gas and fluid in them to regulate buoyancy. Externally they resemble other shelled molluscs, but their anatomy includes features typical of cephalopods: a beak-like jaw, a radula used for feeding, and numerous tentacles. The radula is broad and typically has several rows of teeth; many sources note a characteristic arrangement including nine teeth in some species (radula). Nautiluses possess relatively simple eyes and a pair of gills (a single pair used for respiration) rather than the highly derived camera-type eyes and lungs seen in other cephalopods (gills).

  • Shell: planispiral, chambered, calcified
  • Locomotion: jet propulsion by expelling water
  • Tentacles: many, retractile, without suckers
  • Habitat: typically deep slopes and reef areas in tropical waters

Species, size and distribution

Modern nautiluses are limited in number compared with their fossil relatives. Contemporary treatments commonly recognize several living species—often cited as about six in two genera—with the best-known species being Nautilus pompilius, which occurs across parts of the tropical Indo‑Pacific and has been reported from areas including Western Australia. Sizes vary by species; the largest forms may reach roughly two to three dozen centimetres in shell diameter, while smaller species are considerably less large.

Evolutionary history

Nautiloids have a deep fossil record extending back to the early history of cephalopods. Their fossils document a once-diverse array of forms that dominated many marine ecosystems in the Palaeozoic. Although modern nautiluses represent a small remnant of that diversity, their conservative morphology provides important insights into the early evolution of cephalopods and into how shell-bearing forms behaved and adapted through geologic time.

Human interactions and conservation

Shells of nautiluses have long been collected for decoration, jewelry and scientific study. That trade, combined with localized fishing and habitat pressures, has led to concern for some populations; nautiluses are subject to conservation measures and trade controls in certain regions to prevent overexploitation. Research on living nautiluses informs aquarium husbandry, developmental biology and paleobiology, because they link living cephalopod biology with an extensive fossil legacy.

For further general information consult resources on cephalopod biology and conservation; selected topics and entries are available via links to broad summaries and specialist pages: cephalopods, Nautilidae, biologist perspectives, living fossils, ammonites, Palaeozoic era, species lists, regional records, radula, gill anatomy.