295
Siphonophora
sima basaltic, peridotitic, basic or oceanic crust of the earth, of specific density 3 to 3.3 g cm-3• Name derives from silica-magnesium (hence sima) composition. Compare sial. ~crust.
similarity theory the use of hydraulic models in the solution of hydrodynamic problems requires rules for the way the appropriate scaling has to be done. These
rules are developed in similarity theory. In hydrodynamics the equations are
made nondimensional and in the equations thus transformed certain numbers (nondimensional parameters) occur that should have the same value in the
original (prototype) and the model. ~Froude, ~Rayleigh, ~Reynolds and
~Richardson number.
sinking rate (of particles) sinking rate or sinking velocity of particles in water is
commonly defined as a steady velocity that results from the balance between
the forces of gravity, buoyancy and resistance or drag. The settling velocity of
a sphere as defined by Stokes' law is the most commonly used approximation
of the settling of particles. Whereas it was formerly thought that a slow but
continuous rain of particles reached the sea bottom, it is now clear from sediment trap data that most particles sink rapidly and episodically as aggregates. Such aggregates may be fecal pellets of zooplankton or aggregates formed
by other organic or inorganic processes (~marine snow and ~aggregation).
siphon opening between the fused mantle edges of Bivalvia, often prolonged to a
tube, which can be retracted when the shell is closed. There is an inhalant
and an exhalant siphon, the first leading water with oxygen and food particles into the ventral side of the mantle cavity, the second leading the filtered
water out of the mantle cavity, after it has passed the gill (~ctenidium), which
effectuates the water current by ciliary movement. In some deep-burrowing
Bivalvia the siphons are so large that they can no longer be retracted between
the shell valves.
Siphonophora order of the class Hydrozoa (phylum Cnidaria). Marine pelagic (sometimes floating) colonies of differentiated polyps and medusae, which are all
budded from and stay attached to a main stem. There are several kinds of
these zooids. They can be feeding polyps with one long tentacle with powerful cnidoblasts to collect food. Others without a mouth have the form of a tentacle or a firm gelatinous bract and are for defense. A large gas-filled zooid
functioning as float and sail can be present, and swimming is done by
mouthless medusae. They occur in tropical and subtropical seas, as well as
in deep water. An example is Physalia or Portuguese man-of-war, that has a
large blue float, and is very dangerous for swimmers, because of poisonous
stinging cells (~Cnidaria) . (Figure see p. 296)
Siphonophora
sima basaltic, peridotitic, basic or oceanic crust of the earth, of specific density 3 to 3.3 g cm-3• Name derives from silica-magnesium (hence sima) composition. Compare sial. ~crust.
similarity theory the use of hydraulic models in the solution of hydrodynamic problems requires rules for the way the appropriate scaling has to be done. These
rules are developed in similarity theory. In hydrodynamics the equations are
made nondimensional and in the equations thus transformed certain numbers (nondimensional parameters) occur that should have the same value in the
original (prototype) and the model. ~Froude, ~Rayleigh, ~Reynolds and
~Richardson number.
sinking rate (of particles) sinking rate or sinking velocity of particles in water is
commonly defined as a steady velocity that results from the balance between
the forces of gravity, buoyancy and resistance or drag. The settling velocity of
a sphere as defined by Stokes' law is the most commonly used approximation
of the settling of particles. Whereas it was formerly thought that a slow but
continuous rain of particles reached the sea bottom, it is now clear from sediment trap data that most particles sink rapidly and episodically as aggregates. Such aggregates may be fecal pellets of zooplankton or aggregates formed
by other organic or inorganic processes (~marine snow and ~aggregation).
siphon opening between the fused mantle edges of Bivalvia, often prolonged to a
tube, which can be retracted when the shell is closed. There is an inhalant
and an exhalant siphon, the first leading water with oxygen and food particles into the ventral side of the mantle cavity, the second leading the filtered
water out of the mantle cavity, after it has passed the gill (~ctenidium), which
effectuates the water current by ciliary movement. In some deep-burrowing
Bivalvia the siphons are so large that they can no longer be retracted between
the shell valves.
Siphonophora order of the class Hydrozoa (phylum Cnidaria). Marine pelagic (sometimes floating) colonies of differentiated polyps and medusae, which are all
budded from and stay attached to a main stem. There are several kinds of
these zooids. They can be feeding polyps with one long tentacle with powerful cnidoblasts to collect food. Others without a mouth have the form of a tentacle or a firm gelatinous bract and are for defense. A large gas-filled zooid
functioning as float and sail can be present, and swimming is done by
mouthless medusae. They occur in tropical and subtropical seas, as well as
in deep water. An example is Physalia or Portuguese man-of-war, that has a
large blue float, and is very dangerous for swimmers, because of poisonous
stinging cells (~Cnidaria) . (Figure see p. 296)