nautilis

Nautilus is a genus of marine cephalopods and the only surviving members of the Nautilidae family. They occur in the Indo-Pacific and western Pacific oceans and are instantly recognizable for their distinct planispiral shells. The shell consists of gas-filled chambers and can reach about 20 cm in diameter, though sizes vary among species. The animal occupies the outermost chamber and uses the others to modulate buoyancy.

Anatomy and physiology: Nautiluses have about 90 to 100 tentacles that lack suckers, unlike other cephalopods. They possess relatively simple eyes and a beak-like jaw. A single siphon powers jet propulsion, and a calcium carbonate siphuncle connects the chambers, allowing regulation of gas and fluid to adjust buoyancy.

Habitat and behavior: They inhabit deep reef slopes and drop-offs, typically at depths around 100 to 500 meters, across the Indian Ocean and western Pacific. They are mostly nocturnal, migrating upward at night to forage. Diet consists of crustaceans, small fish, and carrion; they are opportunistic feeders and use ambush or scavenging strategies rather than active pursuit.

Reproduction and life cycle: Nautiluses reproduce sexually; males transfer spermatophores to females. Eggs are laid on the seafloor or in crevices and hatch into small juveniles that resemble adults, indicating direct development. Growth is slow, and lifespans can extend over several decades.

Evolution and paleontology: Nautiloids have a fossil record dating back more than 500 million years, making Nautilus a long-lasting lineage. The group is often described as a living fossil, preserving primitive cephalopod features while existing alongside more derived octopuses and squid.

Conservation: Some Nautilus species are threatened by overfishing, habitat disruption, and collection for shells and display in aquariums. Regional protections exist, but data on population trends are limited and statuses vary by species.