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CORAL REEFS
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green tentacles, which project from the free ends of the
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numerous little upright tubés.
As a matter of fact, only
the surface region of the coral contains living tissues, the -
_
.
Skeleton below being abandoned as the colony grows, and
becoming merely a supporting structure and; incidentally,
the home of innumerable worms; crabs, SpOnges, seaweeds
and many other forms of life.
Unlike the stony corals and
Millepora, the skeleton of this coral is not solid, but is
composed of many tiny calcaredus spicules all fused together.
Exactly similar spicules are found in our own dead—men’s
fingers, but there they are scattered about in a matrix of
spongy tissue.
Another
this type is the
Blue coral, Heliopora, which forms massive colonies often
several feet across ;
if the branches are cut through,
however, the skeleton is seen to be composed of many parallel
tubes like the Organ-pipe
The skelet—on of the Blue
coral is remarkable in that it is cOmposed, _'not of fused
spicules, but of a solid mass of crystalline carb0nate of lime;
Besides the oating Foraminifera; so common' in the
surface waters of the oceans, there are others=which live on
.
the bottom and form
skeletOns, and
_
these,
with the'empty
of the oat‘ing kinds,
form an important constituent of coral réefs in many parts.
,
But the chief factor in the formation of
from
the various types of corals—'and in some areas of equal
or even greater importanCe—are the calcareous coralline sea
weeds or Nullipores. 'Most of these belong to the red
algæ, the most important of them being Lithothamnion
(Plate 61), types of which,
frequently cover the
sea bottom oour own coasts, Melobesia and Lith0phyllum;
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They are all rèddish in colour When aliVe, although the lastwhite when drièd.
,
They are all very widespread, Lithothamnion, for ‘ example,
in great
abundance in the Arctic
offthe British
in the