Portuguese man-of-war
246
structure of cells arranged around one or more chambers (spongocoel). The
structure is supported by an internal skeleton of mostly small calcareous or
siliceous spicules or spongine fibers. The chambers have small pores to the
outside and one larger opening, the inside is lined with flagellated cells
(choanocytes). Through the pores, surrounding water with oxygen and food
is pumped by flagellar beating into the chamber, it is filtered, and than leaves
the sponge through the larger opening of the chamber. There is no organization in the activities in sponges; any part of the body can regenerate. They
are hermaphrodites; fertilized eggs produce flagellated larvae which become
attached to form new sponges. The forms can be simple to very complicated
with networks of canals and chambers. They live sessile in marine and freshwater. Porifera are divided into the classes Demospongiae (with spongine fibers
with or without siliceous spicules), Sclerospongiae (with an external covering
of calcium carbonate), Calcarea or Calcispongiae (calcium carbonate
spicules), and Hexactinellida or Hyalospongiae (glass sponges, with six-pointed siliceous skeletal spicules).
Portuguese man-of-war ~Siphonophora.
potential flow (syn. irrotational flow) flow free of vorticity that can therefore be
described as the gradient of a scalar function, the velocity potential.
potential temperature according to the laws of thermodynamics, water that moves
adiabatically (~adiabatic process) upward or downward, decreases or increases in temperature respectively, because of the change in pressure and the
compressibility of seawater. Therefore temperatures at different depths are not
directly comparable. The potential temperature is defined as the temperature that a parcel of water would have if it were moved adiabatically upward
to the surface. This value, independent of depth, makes comparison possible. The potential temperature (symbol e) can be calculated from the in situ
temperature of deep water, salinity, and pressure (say: depth). The potential
temperature is slightly lower than the temperature in situ.
Prasinophyceae class of the phylum Chlorophyta (kingdom Protoctista), planktonic
algae, usually with four flagella, sometimes two or one. Typical are the small
organic scales, which were used to separate them from the Chlorophyceae.
However, comparable scales have now been found in some Chlorophyceae,
which makes separation of the Prasinophyceae doubtful.
Precambrian ~geological time scale.
precipitation the separation of a substance in solid form from a solution by means
of a reagent. In meteorology, the falling products of condensation in the
atmosphere, such as rain, hail, or snow. Precipitation at sea is difficult to meas-
246
structure of cells arranged around one or more chambers (spongocoel). The
structure is supported by an internal skeleton of mostly small calcareous or
siliceous spicules or spongine fibers. The chambers have small pores to the
outside and one larger opening, the inside is lined with flagellated cells
(choanocytes). Through the pores, surrounding water with oxygen and food
is pumped by flagellar beating into the chamber, it is filtered, and than leaves
the sponge through the larger opening of the chamber. There is no organization in the activities in sponges; any part of the body can regenerate. They
are hermaphrodites; fertilized eggs produce flagellated larvae which become
attached to form new sponges. The forms can be simple to very complicated
with networks of canals and chambers. They live sessile in marine and freshwater. Porifera are divided into the classes Demospongiae (with spongine fibers
with or without siliceous spicules), Sclerospongiae (with an external covering
of calcium carbonate), Calcarea or Calcispongiae (calcium carbonate
spicules), and Hexactinellida or Hyalospongiae (glass sponges, with six-pointed siliceous skeletal spicules).
Portuguese man-of-war ~Siphonophora.
potential flow (syn. irrotational flow) flow free of vorticity that can therefore be
described as the gradient of a scalar function, the velocity potential.
potential temperature according to the laws of thermodynamics, water that moves
adiabatically (~adiabatic process) upward or downward, decreases or increases in temperature respectively, because of the change in pressure and the
compressibility of seawater. Therefore temperatures at different depths are not
directly comparable. The potential temperature is defined as the temperature that a parcel of water would have if it were moved adiabatically upward
to the surface. This value, independent of depth, makes comparison possible. The potential temperature (symbol e) can be calculated from the in situ
temperature of deep water, salinity, and pressure (say: depth). The potential
temperature is slightly lower than the temperature in situ.
Prasinophyceae class of the phylum Chlorophyta (kingdom Protoctista), planktonic
algae, usually with four flagella, sometimes two or one. Typical are the small
organic scales, which were used to separate them from the Chlorophyceae.
However, comparable scales have now been found in some Chlorophyceae,
which makes separation of the Prasinophyceae doubtful.
Precambrian ~geological time scale.
precipitation the separation of a substance in solid form from a solution by means
of a reagent. In meteorology, the falling products of condensation in the
atmosphere, such as rain, hail, or snow. Precipitation at sea is difficult to meas-