Heterotrophic Feeding of Corals
34.1
its tentacles (Porter 1974b). Even if a large strong prey, on being hit by
cnidae, then brake them, it will be most often captured by the polyp
anyway. Paralyzed by cnids, it starts to move chaotically, and then usually
comes up against the polyp again and is captured by the mucus net or by the
tentacles. The swallowing of prey is done with the aid of mucus, which the
polyp sucks into the mouth together with the captured prey. The whole
procedure of capturing and ingesting an animal prey takes 20-40 s. If the
prey is captured by the polyp with short tentacles, which cannot reach the
mouth and bring the captured prey, the polyp's mouth extends and forms a
"tube", which reaches out to the prey and takes it off the tentacle (coral
Favia). The same is done by corals which have a large exposed septal
covered with the epithelium and armed with chidocill. The preys captured
on the surface of this epithelium are ingested by the same procedure (corals
Hydnophora and Leptastrea). Maurice Yonge (1930b) had also described
the mechanism of transport of captured food to the mouth of the polyp by
cilia, which were supposed to be reversing the direction of their beats in the
presence of food. He erroneously concluded that the movement of corund
particles to the mouth of polyps, excited by a drop of fish broth, took place
through the action of cilia, which may reverse the direction of their beats in
a polyp that exhibits the "food reaction". But later it was shown that it was
an artifice. The cilia never reverse their beat, which is directed from the
mouth to the side of the polyp, serving, as their main function, to shed the
sediments (Lewis and Price 1975). But basically Maurice Yonge was rightthe ciliar apparatus indeed participates in the process of feeding of coral
polyps, but its function is quite different. In the inactive, closed state of the
mouth the polyp lets out strips of mucus, which pass between their septae or
between the tentacles. Under the action of the beating cilia the ends of these
strips because whiskered and form the so-called mucus nets a bunch of
sticky finest mucus filaments. The same cilia, beating in one direction,
induce the ciliar currents, which pass through these mucus nets. Thus the
system "ciliar epithelium-mucus net" forms a powerful filtering apparatus.
The mucus nets collect the suspended food particles from the ciliar streams:
slowly moving zooplankters, eggs and cysts, bacteria and pseudoplankton.
Once the mucus net has collected enough food, this is then dragged by the
polyp into its mouth and swallowed (Lewis and Price 1975).
The reaction of swallowing the mucus net and the activation of the
feeding mechanism in the polyp, accompanied by the expansion of tentacles
and the opening of the mouth, is started by the same chemical trigger - the
appearance of a minute concentration of some amino acids, which interact
with the chemoreceptors of the polyp (Mariscal 1971). The traces of amino
acids, which are excreted by zooplankters and other living food objects,
induce the "food reaction" in polyps. The sequence of actions after the start
of the "food reaction" usually results in the capture and swallowing of the
prey by the polyp (Lehnhof 1968; Lehman and Porter 1973; Porter 1974b;
Lewis and Price 1975).
34.1
its tentacles (Porter 1974b). Even if a large strong prey, on being hit by
cnidae, then brake them, it will be most often captured by the polyp
anyway. Paralyzed by cnids, it starts to move chaotically, and then usually
comes up against the polyp again and is captured by the mucus net or by the
tentacles. The swallowing of prey is done with the aid of mucus, which the
polyp sucks into the mouth together with the captured prey. The whole
procedure of capturing and ingesting an animal prey takes 20-40 s. If the
prey is captured by the polyp with short tentacles, which cannot reach the
mouth and bring the captured prey, the polyp's mouth extends and forms a
"tube", which reaches out to the prey and takes it off the tentacle (coral
Favia). The same is done by corals which have a large exposed septal
covered with the epithelium and armed with chidocill. The preys captured
on the surface of this epithelium are ingested by the same procedure (corals
Hydnophora and Leptastrea). Maurice Yonge (1930b) had also described
the mechanism of transport of captured food to the mouth of the polyp by
cilia, which were supposed to be reversing the direction of their beats in the
presence of food. He erroneously concluded that the movement of corund
particles to the mouth of polyps, excited by a drop of fish broth, took place
through the action of cilia, which may reverse the direction of their beats in
a polyp that exhibits the "food reaction". But later it was shown that it was
an artifice. The cilia never reverse their beat, which is directed from the
mouth to the side of the polyp, serving, as their main function, to shed the
sediments (Lewis and Price 1975). But basically Maurice Yonge was rightthe ciliar apparatus indeed participates in the process of feeding of coral
polyps, but its function is quite different. In the inactive, closed state of the
mouth the polyp lets out strips of mucus, which pass between their septae or
between the tentacles. Under the action of the beating cilia the ends of these
strips because whiskered and form the so-called mucus nets a bunch of
sticky finest mucus filaments. The same cilia, beating in one direction,
induce the ciliar currents, which pass through these mucus nets. Thus the
system "ciliar epithelium-mucus net" forms a powerful filtering apparatus.
The mucus nets collect the suspended food particles from the ciliar streams:
slowly moving zooplankters, eggs and cysts, bacteria and pseudoplankton.
Once the mucus net has collected enough food, this is then dragged by the
polyp into its mouth and swallowed (Lewis and Price 1975).
The reaction of swallowing the mucus net and the activation of the
feeding mechanism in the polyp, accompanied by the expansion of tentacles
and the opening of the mouth, is started by the same chemical trigger - the
appearance of a minute concentration of some amino acids, which interact
with the chemoreceptors of the polyp (Mariscal 1971). The traces of amino
acids, which are excreted by zooplankters and other living food objects,
induce the "food reaction" in polyps. The sequence of actions after the start
of the "food reaction" usually results in the capture and swallowing of the
prey by the polyp (Lehnhof 1968; Lehman and Porter 1973; Porter 1974b;
Lewis and Price 1975).