The Chambered Nautilus: A 500-Million-Year-Old Design That Swims by Jet

The chambered nautilus moves like a submarine and is built like one. Its shell is divided into sealed chambers, and by pumping fluid in and out of them, the animal rises and sinks through the deep. Animals like it have been doing this, according to the fossil record, for about 500 million years.

A nautilus. Writers, artists and engineers have long admired its beauty and its swimming. Credit: NOAA.

A mollusk in a shell

The chambered, or pearly, nautilus is a cephalopod, a type of mollusk and a distant cousin of squids, octopuses and cuttlefish. Unlike those color-changing relatives, the soft-bodied nautilus lives inside a hard outer shell, divided into many closed interior chambers.

How it swims

The animal lives in the shell's largest chamber. The rest work like a submarine's ballast tanks. A canal of tissue called the siphuncle (sigh-funk-el) connects them all.

• Moving. Seawater pumps through the living chamber. When the nautilus pulls its body into the chamber, it forces the water out — jet propulsion that pushes it backward and lets it turn.
• Rising and sinking. To move up or down, it uses the siphuncle to draw fluid into, or out of, the smaller sealed chambers, adjusting its buoyancy.

An ancient animal in decline

No regulations currently protect them, but the six living species of chambered nautilus appear to be declining. They are trapped mostly for their attractive shells, and for the shell's inner layer, nacre, which is used as a pearl substitute in jewelry and trinkets. In 2013, NOAA Fisheries funded a University of Washington researcher to study nautilus populations in Fiji and American Samoa; the research should give a clearer picture of how many remain there.

Sources

Based on "What is a nautilus?" from NOAA's National Ocean Service, a work of the United States government in the public domain.