The earth's axis of rotation wobbles like a spinning top. There are two periods (a wobble within a wobble): 19,000 AND 23,000 years. Precession has a profound effect on the earth's climate.
Cephalopods are the most mobile of all mollusks. The gastropods (snails, whelks, conchs, etc.) and nudibranchs are quite mobile and crawl along on their large foot. Some bivalves (clams) can even jet surprising distances by pumping water through their siphons with rapid opening and closing movement of their mantles. Nearly all mollusks are mobile when they first emerge from eggs. Most are simply planktonic, spending a brief period in the water column drifting at the mercy of currents before finding a suitable surface to settle on or burrow into. Many mollusks spend their adult life in a highly sedentary state, attaching themselves permanently to a hard surface with bissus threads, such as mussels, or borrowing into the substrate, such as gribbles, shipworms and many clams. Other species of mollusks are more mobile. They crawl around on their foot, but rarely travel any great distance throughout their lives.
Cephalopods are the jet set. With the exception of the octopus, most spend much of their lives swimming above the bottom. Some squid will even migrate enormous distances in the open oceans. Some large squid can even rival fish, reaching speeds of nearly 20 miles per hour over short periods. Some can even propel themselves out of the water and through the air for considerable distances, reminiscent of flying fish.
Cephalopod swimming is quite different from that of fish. Cephalopods use jet propulsion, pumping water in over their gills and out through a tube called the siphon or funnel. This siphon is a muscular and mobile organ that the animal can use to direct the water jet in almost any direction to steer itself. When observing cephalopods, look for the siphon and watch how the animal moves it.
Jetting isnÕt the only control mechanism in cephalopod swimming, but it is the main engine. Body form, mantle movements, and positioning of tentacles are also important for steering and reducing drag. To begin to appreciate all that is involved in cephalopod swimming, we need to take a look at the basic cephalopod body plan and some of the variations among different cephalopod families.
Cousteau, Jacques Yves and Philippe Diolˇ. 1973. Octopus and Squid, The Soft Intelligence. 1st Ed. Doubleday.Garden City, N.Y.:
Hanlon, Roger T. and John B. Messenger. 1996. Cephalopod Behaviour. New York: Cambridge University Press.
Holloway, Marguerite. 2000. Cuttlefish Say It With Skin. American Museum of Natural History, N. Y. (Online at www.findarticles.com/cf_0/m1134/3_109/61524425/print.jhtml)
Howard, Carl. 1990. The Hood and Tentacles of Nautilus. Unpublished graduate paper, Harvard University, Cambridge, MA.
Lane, Frank. 1974. Kingdom of the Octopus. Sheridan House, N. Y.
Vogel, Steven. 1987. Life in Moving Fluids. Princeton University Press, Princeton, N.J.
http://www.cephbase.utmb.edu/ (May 2003)
-CephBase: General clearinghouse of online articles on cephalopods
http://www.giantsquidcenter.com/ (May 2003)
-Giant Squid: The Last Sea Monster -
www.terrax.org/projects/australia/reef/reeftalk.aspx (May 2003)
-Descibes diving with nautilus in the Coral Sea from a dive cruise boat.
online.sfsu.edu/~biol240/Labs/lab_18molluscs/Pages/cephalopods.html (May 2003)
-Anatomy of cephalopods.
www.cox-internet.com/coop/cephalopoda.html (May 2003)
-Cephalopod evolution and classification.
www.geocities.com/darthdusan/cephalopods.html (May 2003)
-General natural history of cephalopods and history of cephalopod research.
www.seasky.org/reeflife/sea2f2.html (May 2003)
-Pictures and general facts about cephalopods
For Further Info on this Topic, Check out this WWW Site: www.geocities.com/darthdusan/cephalopods.html .
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