Special Sub-Topic: The Nimble Nautilus
|Nautili are cephalopods, and share characteristics with other cephalopods, such as octopi and squids. Which of the following physical traits makes nautili unique from other cephalopods?|
Nautili have external shells. In general, cephalopods have tentacles and can eject ink, and Cephalopoda is a class in the kingdom Mollusca. The nautilus is the only cephalopod with an external shell; however, most cephalopods do have shells, but their shells are internal, beneath layers of soft flesh.
|As is true of most cephalopods, nautili have formed eyes. Which of the following is true of a nautilus' sense of vision?|
The nautilus eye does not have a defined lens, resulting in poor eyesight. The eye of the nautilus is somewhat of an anomaly compared to other cephalopods. Squid and octopi have optical lenses and precise eyesight, while the nautilus has an eye comparable to a pin-hole camera, resulting in simple and imprecise eyesight. Cephalopods do not have corneas, but some squid have the capability of color vision.
|Like most sea creatures, the nautilus is fairly buoyant. How does a nautilus keep from sinking as it moves?|
The nautilus shell is chambered, holding gas inside. The shape of the nautilus shell can be described by a logarithmic spiral, a mathematical curve studied extensively by Jacob Bernoulli. This same spiral can be used to describe the shape of hurricanes and certain galaxies.
|Unlike squid and octopi, nautili are not typically eaten by humans. What does the diet of the nautilus typically consist of?|
Crab and other small crustaceans. The nautilus does not expend much energy with normal bodily functions. Because of this, the nautilus only needs to feed once per month.
|One of the distinguishing physical features of the cephalopod is a set of tentacles. The octopus has eight tentacles of similar length, and the squid has ten tentacles, two of which are much longer than the others. How would one describe the tentacles of the nautilus?|
About 90 tentacles of equal length. Not only does the nautilus have dozens of tentacles more than the squid and the octopus, but its tentacles also differ in structure. Octopi and squid have sucker-pads on their tentacles to grip objects, while nautili do not. Instead, nautili have tentacles with textured ridges, allowing them to grip objects, such as prey.
|You can often find a nautilus in an aquarium. Where in the wild can you find the nautilus?|
Tropical regions of the Indian and Pacific Oceans. The nautilus is found most often in waters surrounding the Australian continent, taking shelter in deep water by day, and hunting in shallow coral formations by night.
|The nautilus has quite a distinctive shape. Which island nation features the shape of the nautilus shell prominently on its national emblem?|
New Caledonia. New Caledonia is a group of islands constituent to France, located off the Australian coast. The nautilus shell is featured on New Caledonia's national emblem, and an artistic rendition of the shell is found on the nation's government flag. New Caledonia features the nautilus because the mollusk is found in the waters surrounding Australia.
|Like most sea creatures, the nautilus has a mechanism allowing it to swim. How does the nautilus push itself through water?|
The nautilus draws water into its body with a siphon, and forces the water back out like a jet. The system of jet propulsion found in the nautilus is quite effective; it uses little energy, and can allow the nautilus to move at a speed of two knots, or about one meter per second.
|The nautilus has distinctive markings on the outside of its shell. What do these decorative markings look like?|
Zebra stripes. The nautilus shell's brown pattern resembles that of a zebra stripe, and its beautiful markings make it a collector's item. The number of nautili, however, has decreased substantially due to overfishing to collect these shells.
|A vital part of the nautilus' digestive system is something called a radula. What is a radula?|
A tongue-like structure covered in tiny teeth. The radula is an anatomical feature present in every mollusk except for the bivalves, which include mussels and clams. The radula is unique; it is found only in the mollusk.
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