Question

A coral stone is made up of
A. Several corallites
B. Corallium
C. A single corallite
D. Both A and B

Answer 1

Hint:- Corals are usually found on rocky sea bottoms that have low sedimentation and dark environments. Thus they are products of sea and are formed of skeletons made up of calcium carbonate.

Complete step-by-step solution:- Corallite is the skeletal cup formed by an individual stony coral poly forms. In a colony many poly are present together. So a coral stone is made up of corallium.
Additional points: The coral belongs to the phylum cnidaria. The general characteristic features of the phylum are:
- This phylum is also called coelenterate and it includes hydroids, jelly fishes, sea-anemone, and corals.
- The colonial forms show two main types of individuals- polyp and medusa. Poly is fixed and cylindrical in shape while medusa is umbrella like and generally free swimming but always solitary.
- Symmetry is usually radial about an oral-aboral axis in both the forms. They have two germ layers i.e. they are diploblastic like the sponges. They have tissue level of organization.
Few examples are:
- Meandrina sinuosa- It is also called the Brain Coral and is found in the Mediterranean Sea and near the coasts of Japan, China and West Indies. The brain corals form a massive rounded encrusting colony (corallum) up to 25 cm or more in diameter.
- Astraea- It is commonly called the Star coral. It grows on rocks in sheltered areas in the tropical seas. It is a colonial form and the colony is fixed and encrusting i.e. spreads over the substratum.

Note:- Each polyp looks like a sea anemone. It secretes a calcareous, cup-like skeleton called the corallite around it for protection. The corallites of all polyps fuse so that the colony presents the appearance of a stone, the corallum. The polyps protrude through pores in the corallum.