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1 _______. A coral attaches itself to a rock or sand. At the top of the polyp tube there is a mouth. The mouth has special tubes, something like feelers, which suck in water plankton and small fish. 2 _______. But how does a coral get calcium for its cup? The warm seawater is full of the calcium needed by a polyp for growing its cup. The softbodied polyp sits in this hard cup which it builds up around itself from calcium. And the hard reef is the cup, or “skeleton” itself. 3 _______. Only in the waters near the equator there is enough calcium, for the reef-builders.
Reef-building corals live in groups or colonies. 4 _______. When the tiny polyps die, their skeletons remain. Other corals attach themselves to hard shells and, later on, also die. A mass of dead coral rises about three feet high in 1,000 years.
Corals belong to the same class of polyps as the sea anemone.
Some green plants live inside the coral and help to get oxygen.
Much calcium, sunlight and algae are necessary for coral skeletons.
Their bright-coloured tubes are always turned towards the sunlight.