Nautiloidea is an ancient subclass of cephalopods. Today only a handful of living species remain— notably Nautilus and Allonautilus—while most nautiloids are known from the fossil record. Modern nautiluses are famous for their external, chambered shell, the shell‑traversing siphuncle and fine control of buoyancy, earning them the nickname “living fossils”.
Ecology & Biology
Buoyancy & respiration: the siphuncle regulates gas and fluid in the chambers, enabling neutral buoyancy and diel vertical movements.
Feeding: scavenges and preys on crustaceans and small benthos; uses dozens of grooved arms and a keratinous beak.
Life history: unusually slow‑growing and late‑maturing for cephalopods; lays large, durable eggs; hatchlings emerge with a miniature shell.
Identification
Typically a planispiral shell with septa forming multiple chambers; often with radiating or wavy colour bands. Eyes are pinhole‑type; arms are numerous and lack suckers; there is no ink sac, unlike squids and octopuses.
Size & Longevity
Length: shell diameter commonly 16–25 cm, larger in some species.
Life: up to 10–20+ years, much longer than most coleoids.
Range & Habitat
Present‑day nautiluses inhabit the Indo‑Pacific, around steep island slopes and outer reef walls. By day they remain mostly at ~200–600 m; at night they may ascend to <200 mto forage.
Conservation & Threats
Threats: shell trade, by‑/trap‑catch, habitat disturbance and ocean acidification.
Management: their late maturity and low fecundity make populations vulnerable; several countries regulate capture and trade.
IUCN: this is a subclass‑level overview. Conservation status is species‑specific; we mark this entry Not Evaluated (NE).
