Spirula

Spirula is a genus of deep-sea cephalopods represented by the living ram’s-horn squid, Spirula spirula. Its small internal shell is coiled into an open spiral and divided into gas-filled chambers.

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Spirula spirula: Spirula spirula is the living ram’s-horn squid, a small deep-sea cephalopod with a chambered internal shell. This species is the genus’s sole living representative.
Nautilus: Nautilus is a cephalopod whose external chambered shell supports buoyancy and protection. Unlike Nautilus, Spirula carries its chambered shell inside its body.
Pelagic zone: The pelagic zone is the open-water region of the ocean, away from the seabed and shore. Spirula inhabits the open water column rather than living on the seafloor.
Pelagic trawling: Pelagic trawling is fishing with a net dragged through open water rather than along the seabed. Trawls have captured living Spirula, providing rare specimens from its deep habitat.
Cephalopod: A cephalopod is a mollusk with arms or tentacles, a prominent head, and a mantle. Spirula belongs to this mollusk class, alongside octopuses, squids, and cuttlefish.
Jet propulsion: Jet propulsion is movement produced by expelling a fluid in the direction opposite to travel. Spirula moves by drawing water into its mantle cavity and expelling it through a funnel.
Deep scattering layer: The deep scattering layer is a zone where dense marine life reflects sonar and often migrates vertically. Spirula’s vertical movements are discussed in relation to this migrating deep-water community.
Beached Spirula shells: Beached Spirula shells are empty internal shells that ocean currents have carried to shore. Their broad coastal distribution once obscured how deep and far offshore the animal lives.
Chambered shell: A chambered shell is divided internally by walls into successive cavities. The partitions in Spirula’s shell form chambers that help regulate buoyancy.
Gas exchange: Gas exchange is the movement of gases between an organism and its environment or internal compartments. Gas exchange across the siphuncle helps adjust fluid and gas in the shell chambers.