Origin of Coral

by Manisha G

The name coral brings to mind the atolls of the South Seas, those narrow reefs surrounding the beautiful transparent waters of the central Lagoon.

There is much misconception concerning the formation of coral, particularly that of the noble coral used in jewels, a coral scientifically known as Corallium Nobile or Corallium rubrum. Generally expressed as being the axial skeleton of the coral polyp, which gives the impression of being an internal skeleton similar to the bones of our bodies, coral is better described as being scaffolding upon the surface of which the boneless animals live as a colony.

The Coral Polyps:

The coral polyp, a primitive type of plant-like animal called a zoophyte, is a small whitish creature about a fifteenth of an inch in diameter. It has a tube like body from the upper rim of which project eight tentacles surrounding the mouth the top portion being known as the coral zone. Thus the animal tends to resemble a sea anemone in miniature.

At the base of tube like body is the basal disc, which in the case of colonies is connected by a layer of communicating canals of living tissue, called the hydrorhiza, to the enteron or stomach, of each individual member of colony. The hydrorhiza are embedded in a gelatinous mass, termed the coenosarc, and which itself is covered by a skin like membrane called the perisac. Thus the whole colony forms the single entity and it is from the lower surface of the coenosarc and from the base of the polyp, the coral is formed.

Reproduction may be sexually from ova and sperm, or by budding. In the colonies themselves there is always rigorous segregation of the sexes. Usually a colony consists of individuals of one sex only, and if the colony is bi-sexual it is found that the sexes occupy separate braches. The male individual discharges his fertilizing cells into the water, some of which find their way into the body of a female and penetrate the eggs already prepared for fertilization.

The fertilized eggs of microscopic size are ejected into the water by the female and they subsequently develop into free-swimming medusal forms for the surviving medusal forms, the mortality is high, it sinks and attach themselves by their convex surfaces to a stone, rock, crab, bottle but never bare metal. Once the swimming form has attached itself securely to its new home, a knob appears on its free end, which quickly enlarges, and it soon becomes a fully developed polyp. Calcium carbonate is secreted around the point of attachment forming the nucleus of the coral structure, and of a new colony. The coenosarc grows over the calcareous deposit and the second stage of reproduction commences.

This is by a species of budding or self-germination of the polyp itself within the coenosarc – a knob – like protuberance forming and then developing into a polyp. Thus the newly formed colony is gradually populated. As the colony continues to grow, the coenosarc spreads to accommodate the new inhabitants, and in order to provide living room for them is continually separating calcium carbonate from the sea water, and redepositing the mineral in the form of specules of a calcite as coral.

At first, this deposition of lime is confined to the point of attachment of the original polyp and then the skeleton commences to extend into a column upon which a number of secondary polyps form. Some of these lateral polyps also start to shoot out sideways and this produces a branch-like form to the whole colony. The branches spread out as widely as possible and are haphazardly arranged, but no two branches spring from the same point of incidence. These branches may be more or less straight or may be twisted and turn about in an irregular manner; they may also produce secondary branches and so on.

Each branch becomes smaller than its parent and terminates with the rounded blunt point covered by a very sensitive layer of coenosarc, which project beyond the branch itself.

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