Reynolds stress
270
the water. The transition from a laminar current to turbulence occurs above a
critical value of Re.
Reynolds stress the internal stress due to turbulent exchange of momentum
between the layers of a fluid.
RheicOcean (syn. Proto-Tethys) the ocean which separated the Baltic (N. Europe)
and Laurentian (N. America and Greenland) plates from the southern continents and S. Europe. The Rheic Ocean became closed during the late
Carboniferous.
rheotaxis the movement of an organism directed by a water current. It is difficult to imagine how pelagic animals sense the direction of a current. Benthic
animals may move against a current towards food, but in such a case it is
more likely that chemotaxis is involved. Good examples of rheotaxis are therefore not available from the marine environment.
rheotropism growth as a response to currents, can be found in sessile organisms,
e.g., transversal rheotropism in hydroids, Bryozoa and horny corals, whose
colonies grow perpendicular to the main direction of currents.
Rhizocephala order of the class Cirripedia (subphylum Crustacea, phylum Arthropoda).
Parasitic barnacles, almost exclusively on decapod crustaceans. The typical
cirripedian larvae (cypris) attaches itself to the host and than develops into
a root-like structure within that host. This structure penetrates almost all
the hosts tissues, and in this stage it cannot be recognized as a crustacean,
as it is devoid of any clear characters. When mature they form an external
sac, which contain the eggs. They are hermaphrodites or of separate sex. In the
latter case the parasitic form is the female, which is fertilized by absorbing
free-living larval males. It often castrates the host and inhibits the molting.
Most species are marine, and only a few live in freshwater. Example:
Saccu/ina, parasite of the shore crab.
Rhizomastigina unicellular organisms with one or two flagella, and the whole surface of the body permanently ameboid. ~Protozoa.
Rhizopoda (syn. Sarcodina) phylum of the kingdom Protoctista. Unicellular organisms with mostly naked cells, which locomote by means of lobe-like projection of the flexible cell wall (pseudopodia). Sometimes the cell is enclosed in
a test; flagella are absent. Usually they are not parasitic, have no meganucleus, and, though they may have a phase of sporulation, do not form large
numbers of spores after syngamy. A well-known class is the Amoebida.
270
the water. The transition from a laminar current to turbulence occurs above a
critical value of Re.
Reynolds stress the internal stress due to turbulent exchange of momentum
between the layers of a fluid.
RheicOcean (syn. Proto-Tethys) the ocean which separated the Baltic (N. Europe)
and Laurentian (N. America and Greenland) plates from the southern continents and S. Europe. The Rheic Ocean became closed during the late
Carboniferous.
rheotaxis the movement of an organism directed by a water current. It is difficult to imagine how pelagic animals sense the direction of a current. Benthic
animals may move against a current towards food, but in such a case it is
more likely that chemotaxis is involved. Good examples of rheotaxis are therefore not available from the marine environment.
rheotropism growth as a response to currents, can be found in sessile organisms,
e.g., transversal rheotropism in hydroids, Bryozoa and horny corals, whose
colonies grow perpendicular to the main direction of currents.
Rhizocephala order of the class Cirripedia (subphylum Crustacea, phylum Arthropoda).
Parasitic barnacles, almost exclusively on decapod crustaceans. The typical
cirripedian larvae (cypris) attaches itself to the host and than develops into
a root-like structure within that host. This structure penetrates almost all
the hosts tissues, and in this stage it cannot be recognized as a crustacean,
as it is devoid of any clear characters. When mature they form an external
sac, which contain the eggs. They are hermaphrodites or of separate sex. In the
latter case the parasitic form is the female, which is fertilized by absorbing
free-living larval males. It often castrates the host and inhibits the molting.
Most species are marine, and only a few live in freshwater. Example:
Saccu/ina, parasite of the shore crab.
Rhizomastigina unicellular organisms with one or two flagella, and the whole surface of the body permanently ameboid. ~Protozoa.
Rhizopoda (syn. Sarcodina) phylum of the kingdom Protoctista. Unicellular organisms with mostly naked cells, which locomote by means of lobe-like projection of the flexible cell wall (pseudopodia). Sometimes the cell is enclosed in
a test; flagella are absent. Usually they are not parasitic, have no meganucleus, and, though they may have a phase of sporulation, do not form large
numbers of spores after syngamy. A well-known class is the Amoebida.