Siphuncle - Citizendia

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Tissue is a cellular organizational level intermediate between cells and a complete organism The cephalopods ( Greek plural (kephalópoda "head-feet" are the Mollusc class Cephalopoda characterized by Molluscs are animals belonging to the phylum Mollusca. There are around 250000 extant Species within the phylum with an estimated 70000 Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. Ammonites are an extinct group of marine animals of the subclass Ammonoidea in the class Cephalopoda phylum Belemnites (or belemnoids are an extinct group of marine Cephalopod, very similar in many ways to the modern Squid and closely related to the modern Cuttlefish Nautilus (from Greek ναυτίλος, 'sailor' is the common name of any marine creatures of the Cephalopod family Nautilidae, the sole Cuttlefish are marine animals of the order Sepiida belonging to the Cephalopoda class (which also includes Squid, Octopuses Spirula spirula is a Species of deepwater Squid -like Cephalopod. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the walls dividing the chambers of the shell.

In living cephalopods the siphuncle is used primarily in emptying water from new chambers as the shell grows. Essentially what happens is the cephalopod increases the saltiness of the blood in the siphuncle, and the water moves from the more dilute chamber into the blood through osmosis. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products At the same time gas, mostly nitrogen, oxygen, and carbon dioxide, diffuses from the blood in the siphuncle into the emptying chamber, filling it up with gas. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Note that the cephalopod does not pump up the shell; the gas moving into the chamber is a passive process, instead the energy is used in absorbing the water from the chamber.

An image showing the siphuncle, the tube which connects the current living shell to the previous ones.

Removing water from the chambers of the shell reduces the overall density of the shell, and thus the shell behaves as a flotation device comparable to the swim bladder in bony fish. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different gas bladder (also fish maw, less accurately swim bladder or air bladder) is an internal organ that contributes to the ability of a Fish Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Typically, cephalopods maintain a density close to that of sea water, allowing them to swim with the minimum of effort. In the geologic past, many cephalopods grew to an enormous size (over ten meters in length) thanks to this.

What the siphuncle is generally unable to do is provide a way to change rapidly the density of shell and thus cause the animal to rise or sink at will; rather, the animal must swim up or down as required.

The siphuncle in fossil cephalopods is assumed to have worked in the same general way. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. The siphuncle itself only rarely gets preserved, but many fossils show the holes, called septal necks, through which the siphuncle passed. In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral surface. In some fossil straight shelled nautiluses cylindrical calcareous growths ("siphuncular deposits") around the siphuncle can be seen towards the apex of the shell. These were apparently counterweights for the soft body at the other end of the shell, and allowed the nautilus to swim in a horizontal position. Without these deposits, the apex of the buoyant shell would have pointed upwards and the heavier body downwards, making horizontal swimming difficult.

See also