Find the word definition

The Collaborative International Dictionary
siphuncle

Siphon \Si"phon\, n. [F. siphon, L. sipho, -onis, fr. Gr. ??? a siphon, tube, pipe.]

  1. A device, consisting of a pipe or tube bent so as to form two branches or legs of unequal length, by which a liquid can be transferred to a lower level, as from one vessel to another, over an intermediate elevation, by the action of the pressure of the atmosphere in forcing the liquid up the shorter branch of the pipe immersed in it, while the continued excess of weight of the liquid in the longer branch (when once filled) causes a continuous flow. The flow takes place only when the discharging extremity of the pipe ia lower than the higher liquid surface, and when no part of the pipe is higher above the surface than the same liquid will rise by atmospheric pressure; that is, about 33 feet for water, and 30 inches for mercury, near the sea level.

  2. (Zo["o]l.)

    1. One of the tubes or folds of the mantle border of a bivalve or gastropod mollusk by which water is conducted into the gill cavity. See Illust. under Mya, and Lamellibranchiata.

    2. The anterior prolongation of the margin of any gastropod shell for the protection of the soft siphon.

    3. The tubular organ through which water is ejected from the gill cavity of a cephaloid. It serves as a locomotive organ, by guiding and confining the jet of water. Called also siphuncle. See Illust. under Loligo, and Dibranchiata.

    4. The siphuncle of a cephalopod shell.

    5. The sucking proboscis of certain parasitic insects and crustaceans.

    6. A sproutlike prolongation in front of the mouth of many gephyreans.

    7. A tubular organ connected both with the esophagus and the intestine of certain sea urchins and annelids.

  3. A siphon bottle.

    Inverted siphon, a tube bent like a siphon, but having the branches turned upward; specifically (Hydraulic Engineering), a pipe for conducting water beneath a depressed place, as from one hill to another across an intervening valley, following the depression of the ground.

    Siphon barometer. See under Barometer.

    Siphon bottle, a bottle for holding a["e]rated water, which is driven out through a bent tube in the neck by the gas within the bottle when a valve in the tube is opened; -- called also gazogene, and siphoid.

    Siphon condenser, a condenser for a steam engine, in which the vacuum is maintained by the downward flow of water through a vertical pipe of great height.

    Siphon cup, a cup with a siphon attached for carrying off any liquid in it; specifically (Mach.), an oil cup in which oil is carried over the edge of a tube in a cotton wick, and so reaches the surface to be lubricated.

    Siphon gauge. See under Gauge.

    Siphon pump, a jet pump. See under Jet, n.

Wiktionary
siphuncle

n. A strand of tissue passing longitudinally through the shell of a cephalopod mollusk, used primarily in emptying water from new chambers as the shell grows.

Wikipedia
Siphuncle

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. 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.

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. At the same time gas, mostly nitrogen, oxygen, and carbon dioxide, diffuses from the blood in the siphuncle into the emptying chamber. 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.

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. 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 (perhaps approaching ten meters in length) thanks to this.

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

The siphuncle found in fossilised cephalopods is assumed to have worked in the same general way. The siphuncle itself only rarely gets preserved, but many fossils show the holes, called septal necks (or siphuncle notches), 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. The siphuncle of the Endocerida also contained much of the organisms' body organs.

Usage examples of "siphuncle".

A central well looked down through two or three siphuncle holes to the chamber where the orthocone creature now resided, with a stout railing as protection against any random heavings of those thousands of tons of living flesh.