Organ pipe coral is
A. Astraea
B. Tubipora
C. Fungia
D. Meandrina

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Hint:Organ pipe corals are the marine soft corals. They are found on reefs in the shallow water of the Indian and Pacific oceans. They have green-colored tentacles and a red-colored skeleton.

Complete answer:Corals are made up of tiny animals called coral polyps which grow as colonies. Polyps are the simple cup-like structure that has one open end which acts as a mouth for the coral surrounding by a ring of tentacles. The cup acts as a stomach for the coral that contains digestive as well as reproductive tissues. These coral polyps first attach to a stone on an ocean bed and secrete a shell around it which is known as a solitary coral. These further divide and grow by making more identical polyps and more shells around them which are known as coral reefs. The energy required for building a reef is obtained by a symbiotic relationship between the coral and algae called zooxanthellae. Zooxanthellae live inside the corals that use energy from the sun to perform photosynthesis and produce up to 95 percent of the food that corals need. Corals in return produce nutrients like carbon dioxide, phosphorous, and nitrogen required for algae and also provide them with a safe environment to live in. As this benefits both corals and algae it is known as a symbiotic relationship. The algae are responsible for the different colors of the corals. Corals are of two types: hard or stony corals form a skeleton and form a reef and soft corals that do not form a skeleton and do not form a reef. This classification is also based on the symmetry of the polyps. Soft corals are octocorallia i.e. their symmetry is divisible by 8 whereas stony corals are hexacorallia i.e. their symmetry is divisible by 6.
In the case of Organ pipe coral (Tubipora musica), they are soft corals i.e. octacoralia that deposits a red color skeleton. It is a member of Tubiporidae family. Genus tubipora comprises soft corals. Organ pipe corals form a red-colored skeleton made up of calcium carbonate and the tentacles are green in color. Once, the soft tentacles part die the corals remain with a red-colored pipe-like structure i.e. calcium carbonate skeleton.

Hence, the correct option will be option B- Tubipora.

Note: Astraea is a genus of sea snails. Genus fungia is a genus that has stony corals while Meandrina is a genus for stony colonial corals. Kingdom classification has two similar terms ‘Kingdom Fungi’ and ‘Genus Fungia’. These two are different terms genus Fungia belongs to Kingdom Animalia.