nautilids

Nautilids are a small, ancient lineage of shelled cephalopods within the subclass Nautiloidea. Today they are represented by two extant genera, Nautilus and Allonautilus, with a limited number of living species. The most distinctive feature of nautilids is their external coiled shell, divided into gas-filled chambers that provide buoyancy. The animal maintains buoyancy by regulating the relative amounts of gas and liquid in these chambers through a siphuncle that runs through the shell’s compartments. Unlike most other cephalopods, nautilids have numerous tentacles around the mouth and lack the suckers or hooks found on octopuses and squids. Their eyes are relatively simple, and the shell remains the primary protective and buoyant structure.

Ecology and behavior: Nautilids inhabit warm, tropical and subtropical waters of the Indo-Pacific, often on rocky slopes or in caves at depths generally around 200–500 meters. They are largely nocturnal, feeding on small invertebrates such as crustaceans, as well as carrion. They capture prey with their tentacles and move by jet propulsion, adjusting buoyancy as needed. Reproduction is slow, with females laying eggs that develop into immobile, benthic juveniles rather than free-swimming larvae in many species.

Fossil record and significance: Nautilids have a long fossil history, dating back to the Late Cambrian. They are among the few surviving nautiloids and are often described as living fossils because their external shell form and overall body plan have changed little over hundreds of millions of years.

Conservation: Nautilids are affected by overharvesting for their shells in some regions and by habitat disturbance. Protection and management vary by range, but regional declines have been reported where collection is unregulated.