The close coexistence of two organisms of different species that benefit from each other is called symbionts. Hydra obtains food and oxygen from algae. The CO2 and waste products produced by hydra growth are fed to the algae. As a result, Hydra benefits and life becomes easier. Hence hydra is called a mythic organism. Green hydra called Chlorohydra viridissima forms mitosis.

1. Food: Hydra consumes excess food produced by algae in the process of photosynthesis. When the algae die, the corpse is used by the hydra as food.
2. Obtaining O2: Hydra uses the O2 produced by algae in the process of photosynthesis. Dr. Siddiq Publications
3. Excretion of waste products: Hydra produces nitrogenous waste products in the process of respiration. Algae consume these waste materials and free the hydra waste.

1. Shelter: Algae take shelter in hydra’s endodermal muscle cells.
2. CO2 Acquisition: Algae use the CO2 produced in hydra respiration for photosynthesis.
3. Nitrogen acquisition: The nitrogenous waste products of hydra metabolism are used by algae to produce carnivorous food.
4. Protection from environmental stress: Algae take shelter in hydra’s body. So it is protected from heat, stress, dryness etc. Dr. Siddiq Publications

The Greek word Symbioum means live together. The close co-existence of two organisms of different species that benefit from each other is called mytosymbiosis. Algae Zoochlorella and green hydra Chlorohydra viridissima form mitotic organisms. Again, sea urchins and clownfish form a symbiotic relationship. Algae parts are transmitted to the next generation along with hydra eggs. So algae is called lifelong paying guest. How hydra and algae benefit is discussed below.Dr. Siddiq Publications
How Algae Benefit
1. Shelter: Algae take shelter in hydra’s endodermal muscle cells.
2. CO2 Acquisition: Algae use the CO2 produced in hydra respiration for photosynthesis.
3. Nitrogen acquisition: The nitrogenous waste products of hydra metabolism are used by algae to produce carnivorous food.
4. Protection from environmental stress: Algae take shelter in hydra’s body. So it is protected from heat, stress, dryness etc. Dr. Siddiq Publications
How does Hydra benefit?
1. Food: Hydra consumes excess food produced by algae in the process of photosynthesis. When the algae die, the corpse is used by the hydra as food.
2. Obtaining O2: Hydra uses the O2 produced by algae in the process of photosynthesis. Dr. Siddiq Publications
3. Excretion of waste products: Hydra produces nitrogenous waste products in the process of respiration. Algae consume these waste materials and free the hydra waste.

Most hydra are dioecious, but some hydra are monoecious. Self-indulgence is a sexual process. The union of sperm and ovum of the same animal is called insemination. Even though hydra is bisexual, self-fertilization does not occur. In the same hydra, spermatozoa and ova are produced in two different seasons. In hydra the eggs are immature at the time when the sperm are mature. Again, when the egg is mature the sperm is immature. Therefore sperm and egg of the same hydra can never meet. This is why self-fertilization does not occur in hydra. In hydra, only purification occurs. Dr. Siddiq Publications

Embryo elongates inside the cyst at favorable temperatures during spring. In the embryo, the mouth opening, hypostome, trachea and foot wheel are formed. This condition of the fetus is called hydrula. Dr. Siddiq Publications

In the process of gastulation, the cells of the blastomere form a two-layered nerate and spherical structure. This is called gastrula dasha. The gastrula of hydra is called stereogastula because it is attached to the mother body. The outer layer of the gastrula is called ectoderm and the inner layer is called endoderm. Between the ectoderm and endoderm are jelly-like acellular mesoglia. The gastrular cavity is called the primitive cilenteron.

In the blastulation process, the cells of the morula stage are arranged in a certain layer and form a hollow spherical structure. This is called blastula dasha. The cavity in the center of the blastula is called the blastocell. The blastular wall is called blastoderm and the cells are called blastomere.

The zygote divides repeatedly by cleavage to become multicellular, sterile and round cells. This is called Marula Dasha. Two types of cells are formed in marula dasha. Micromere and macromere. Dr. Siddiq Publications

Development: The zygote divides repeatedly and turns into a full-fledged organism is called development. The division of the zygote in Hydra is holoblastic or complete. The stages of its development are as follows.
1. Morula stage: The zygote divides repeatedly by cleavage to become multicellular, sterile and round cells. This is called Marula Dasha. Two types of cells are formed in marula dasha. Micromere and macromere. Dr. Siddiq Publications
2. Blastula stage: In the blastulation process, the cells of the morula stage are arranged in a certain layer and form a hollow spherical structure. This is called blastula dasha. The cavity in the center of the blastula is called the blastocell. The blastular wall is called blastoderm and the cells are called blastomere.
3. Gastrula Stage: In the process of gastulation, the cells of the blastomere form a two-layered nerate and spherical structure. This is called gastrula dasha. The gastrula of hydra is called stereogastula because it is attached to the mother body. The outer layer of the gastrula is called ectoderm and the inner layer is called endoderm. Between the ectoderm and endoderm are jelly-like acellular mesoglia. The gastrular cavity is called the primitive cilenteron.
4. Cyst: Gastula is surrounded by spiny sheath made of chitin. It is called a cyst.
5. Hydrilla: Embryo elongates inside the cyst at favorable temperatures during spring. In the embryo, the mouth opening, hypostome, trachea and foot wheel are formed. This condition of the fetus is called hydrula. Dr. Siddiq Publications