An ancient group of marine animals, nautiloids have changed very little in more than 500 million years.
Nautiloids were among the first swimming predators. They use "water-jet propulsion" to swim, and have shells with separate chambers for buoyancy control. Like their octopus relatives, nautiloids have tentacles around the mouth.
Nautiloids (NAWT-ih-loyds): swimming marine mollusks with chambered external shells
New feature:
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Chambered shell for buoyancy control; fluid levels within separate chambers regulate buoyancy at various depths and pressures
PICTURE CAPTIONS:
- siphuncle: a fleshy tube that links shell chambers; used to adjust fluids within chambers to regulate buoyancy
- suture: a curved seam that marks the place where the septum joins the outer shell wall; strenghens shell
- septum a shell partition that separates chambers; forms behind the animal as it grows forward in the shell; strenghtens shell
- Diagram showing common ancestry and evolution of nautiloids, ammonoids, and squid/octopus from organisms with a shell modified for buoyancy, head with tentacles, and water-jet propulsion. Evolution of maximum of ten arms is where ammonoids and squid/octopus branch off.