The chambered nautilus, Nautilus pompilius, is one of six living nautilus species that represent the last of a vast array of ancient shelled cephalopods.
On your next Wild Reef visit, just before you get to the sharks, stop at the darkened habitat and crane your neck a bit to find Shedd's nautiluses near the surface of the water.
Like their more modern relatives, the soft-bodied octopuses, squids and cuttlefish, which round out the taxonomic class Cephalopoda, nautiluses have large eyes in a large head, a tooth-lined radula inside a beak for chomping on prey, tentacles, two pairs of gills and a siphon for jet-skiing through the water. And encased in the beautiful brown-banded spiral of a shell is a brain capable of learning and remembering.
The fossil record indicates that today’s nautiluses are pretty much the same as the chamber-shelled cephalopods that evolved in Late Cambrian seas some 500 million years ago. Over the next 200 million years or so, nautiloids diversified into many forms, including some with straight 8-foot-long shells, coiled ammonites the size of manhole covers, and the family Nautilidae, which includes the chambered nautilus. They formed a group of large, very mobile predators that consumed anything they could catch.
Today’s nautiluses are also opportunist feeders, preying on shrimp and small fishes. At Shedd, our nautiluses eat clam, shrimp, smelt, silversides, mackerel, capelin and herring. Aquarist Laura Hilstrom lets these cephalopods demonstrate their feeding techniques.
At the habitat, she slides open the cobalt blue plexiglass covers that create a low-light, deep ocean environment for the animals. They are anchored to its rocky reef wall, but when Laura attaches a small shrimp to the end of a wand-like plexi feed stick and swishes it in the water, they bob over. “A nautilus moves faster in reverse, when its siphon, called a hyponome, is a straight tube for a jet of water, than it does going forward, when the hyponome is bent underneath it,” she says. In the wild, ae nautilus would also use the siphon to blow water to uncover crabs and even carrion in sand or fine coral rubble on the reef floor.
Unlike the sharp-eyed octopuses, nautiluses have simple pinhole-camera-like eyes that cannot focus. This isn’t a big issue for an animal that moves mainly in reverse, but it requires a different hunting strategy. Laura explains that a nautilus relies on its highly developed olfactory sense to pick up the smell of prey. Its “nose” is divided among conspicuously ridged paired tentacles, one in front of and one behind each eye, that have chemical sensors for detecting prey and predators. The rest of a nautilus’s nearly 90 tentacles are divided into either longer ones, for gripping, or shorter ones ringing the mouth area to convey food to the beak concealed under the animal’s mantle. Instead of suction disks, the tentacles have grooves and ridges that adhere so strongly to surfaces, from reef walls to fish scales to skin, that they feel sticky.
One nautilus grabs the shrimp and pumps its gills so hard in excitement from the successful “hunt” that it rocks in the water. When it calms down, it glides back to the rockwork, anchors and begins to devour its meal, shell and all. In addition to the calcium it gets from the shrimp shell, the nautilus absorbs the liquid calcium that Laura adds to the water to ensure that her charges have healthy shell growth.
Cephalopods have a reputation for intelligence, based heavily on octopuses, which, with their combination of problem-solving abilities and truly superhuman dexterity, give us something to measure their smartness against our own. It’s trickier to plumb the depths of the more physically contained nautilus’s intellect.
“It’s hard to compare,” says Laura. “A nautilus has a simple brain, with low learning ability. But even though they are probably not as intelligent as octopuses, I would say that they are very curious. I have to be careful what items I put in the exhibit because a nautilus will come over and check it out. They love to chew, so I have to make sure that one won’t ingest anything that isn’t food.”
Studies have shown that nautiluses have short-term memory ability on a par with octopuses, enabling them to learn to associate cues with food. Laura can back this fact up: “I had one group that would come to the surface for food after being conditioned to recognize that three taps with the tongs on the side of the exhibit meant feeding time.” One can only imagine a herd of hungry nautiluses bobbing through the water toward the aquarist on cue.
Karen Furnweger, web editor