Musculo-epithelial cells are located throughout the epidermis. The cells look columnar. The outside of each cell is wide and free and the inside is closed and narrow. There are two muscle enhancers on the inside. It is also called muscle tail. Within the muscle tail are the contractile fibers myoneme. The cytoplasm of the cell contains a nucleus, mucous material and granular glands. The cells lining the musculature are large, flattened and contain nidocytes. Mucin is secreted from the mucous material and granules from the granular glands. Muscle sheath cells are interconnected to form an integral sheath.
Musculoskeletal function
(i) Musculature protects the body by creating a body covering.
(ii) Myoneme causes contraction-expansion of the body.
(iii) Mucous gland secretion keeps the body slippery.
(iv) It bears nematocysts.
(v) It helps in movement by contraction-expansion.
(vi) Mucous granules secreting sap form the cuticle.
(vii) It contains nidoblasts.
(viii) Keeps the body attached to an object.
(ix) Part rich in mucous granules participates in digestion.

The round and pressed part in the lower part of the body is the sole of the foot. A sticky substance secreted from the soles of the feet keeps the hydra attached to objects. Bubbles help float in water. It helps the hydra to move by forming a membrane. Hydra displays gliding movements with the help of discs. Dr. Siddiq Publications

The part between the stem and the foot is the petiole. It is narrow, narrow and contractile. It connects the body and the foot.

During hibernation and winter, temporary genitalia are formed on the body of the metamorphosed hydra. The upper part of the body contains the spermatozoa and the lower part the ovary. The testicles produce sperm and the ovaries produce eggs. Participates in sperm and egg production.

Favorable environment or environment with sufficient food during summer. Hydra gains physical growth by consuming food. As a result, one or more buds are formed in the middle region of the body. Each bud matures and gives birth to a new hydra. This is one of hydra’s asexual reproduction methods. Dr. Siddiq Publications

At the base of the hypostome there are 6-10 slender, long, hollow and contractile-expanding sturgeon. Each karshika is twice or thrice as long as the body. The outer wall of Karshika consists of batteries of small nematocysts like tumors. Karshikas are arranged in a circle. It participates in food intake, movement and self-defense.

The word Hypostome is formed from hypo meaning below and stoma meaning mouth. The upper part of the body has a mouth opening. The small and twisted contractile organ below the stoma is called the hypostome. Stomata receive food, water and oxygen. It expels undigested or waste material.

External structure of Hydra
Hydra is a small tube-shaped animal. When expanded they are about 1-3 cm long and 1 mm wide. When removed from the water, they turn into a soft and shapeless lump. Hydra’s body consists of three parts. Hypostome, body stem and foot.
1. Hypostome: The word Hypostome is formed from hypo meaning below and stoma meaning mouth. The upper part of the body has a mouth opening. The small and twisted contractile organ below the stoma is called the hypostome. Stomata receive food, water and oxygen. It expels undigested or waste material.
2. Body: The entire body except the hypostome and the base is called the body. Different parts of the body-
(i) Sterile: At the base of the hypostome there are 6-10 slender, long, hollow and contractile-expanding sturgeon. Each karshika is twice or thrice as long as the body. The outer wall of Karshika consists of batteries of small nematocysts like tumors. Karshikas are arranged in a circle. It participates in food intake, movement and self-defense.
(ii) Mukul: Favorable environment or environment with sufficient food during summer. Hydra gains physical growth by consuming food. As a result, one or more buds are formed in the middle region of the body. Each bud matures and gives birth to a new hydra. This is one of hydra’s asexual reproduction methods. Dr. Siddiq Publications
(iii) Genitalia: During hibernation and winter, temporary genitalia are formed on the body of the metamorphosed hydra. The upper part of the body contains the spermatozoa and the lower part the ovary. The testicles produce sperm and the ovaries produce eggs. Participates in sperm and egg production.
(iv) Pedicel: The part between the stem and the foot is the petiole. It is narrow, narrow and contractile. It connects the body and the foot.
3. Padachakti: The round and pressed part in the lower part of the body is the sole of the foot. A sticky substance secreted from the soles of the feet keeps the hydra attached to objects. Bubbles help float in water. It helps the hydra to move by forming a membrane. Hydra displays gliding movements with the help of discs. Dr. Siddiq Publications
Internal structure of Hydra
Longitudinal or transverse section of Hydra showing the body wall and gastrovascular or coelenteron. The body wall consists of two cell layers. Epidermis (embryonic ectoderm) and gastrodermis (embryonic endoderm).
The outermost cell layer of the body wall is called the epidermis. The thickness of the epidermis is one-third that of the body wall. It contains seven types of cells. Muscle sheath cells, interstitial cells, sensory cells, nerve cells, glandular cells, germ cells and nidoblasts.
1. Musculo-Epithelial cells: Musculo-epithelial cells are located throughout the epidermis. The cells look columnar. The outside of each cell is wide and free and the inside is closed and narrow. There are two muscle enhancers on the inside. It is also called muscle tail. Within the muscle tail are the contractile fibers myoneme. The cytoplasm of the cell contains a nucleus, mucous material and granular glands. The cells lining the musculature are large, flattened and contain nidocytes. Mucin is secreted from the mucous material and granules from the granular glands. Muscle sheath cells are interconnected to form an integral sheath.
Musculoskeletal function
(i) Musculature protects the body by creating a body covering.
(ii) Myoneme causes contraction-expansion of the body.
(iii) Mucous gland secretion keeps the body slippery.
(iv) It bears nematocysts.
(v) It helps in movement by contraction-expansion.
(vi) Mucous granules secreting sap form the cuticle.
(vii) It contains nidoblasts.
(viii) Keeps the body attached to an object.
(ix) Part rich in mucous granules participates in digestion.
2. Interstitial cell: Interstitial cells are located in clusters between muscle cells. It is called Reserve cell or Stem cell or multipotent cell. The cells appear round, oval or triangular in shape. Each cell contains a nucleus, numerous mitochondria, endoplasmic reticulum, lysosomes, ribosomes etc. It has totipotency capability. So it transforms into any other cell as needed. The diameter of the cells is 5 μm.
Function of interstitial cells
(i) A cell can transform into any other cell.
(ii) It participates in hydra regeneration, growth, gonad and bud formation.
(iiii) After 45 days, when body cells are destroyed, interstitial cells fill the space.
3. Sensory cell: Sensory cells are scattered in the spaces between the muscle covering cells. However, it is numerous in karshika, hypostome, feet. The cells appear narrow, elongated and spindle-shaped. That is, the middle part is wide and both ends are narrow. Each cell has cytoplasm and a swollen nucleus. It has contractile membranes on the outside and sensory nerves on the inside. It is sensitive to light, heat, touch, chemicals etc. Dr. Siddiq Publications
Function of sensory cells
(i) It receives different types of stimuli from the environment.
(ii) It participates in self-defense.
(iii) It helps in selection of accommodation.
(iv) It selects food.
4. Nerve cells: Nerve cells are located under the epidermis near the mesoglia. The cells appear maculate or polygonal. Cytoplasm and nucleus are present in the cell. Each cell has two or more branched nervous systems. Nervous systems combine to form the neural network. Dr. Siddiq Publications
Nerve cell function
(i) It receives nerve impulses from sensory cells and generates reports.
(ii) It facilitates coordination between different cells.
5. Gland cell: Gland cells are located in the peduncle, hypostome and peduncle. Cells may appear cylindrical, granular, or oval. It contains mucous glands, enzyme glands and glands that secrete mucus.
Function of glandular cells
(i) A cell helps in digestion of food.
(ii) The secreted sticky juice keeps the hydra attached to an object.
(iii) It helps in locomotion by creating momentum.
(iv) Helps hydra to float in water by creating bubbles.
6. Germ cell: During the reproductive season, spermatozoa and ovum are formed from interstitial cells in the hydra body stem. The testes are above and the ovaries are below. The testicles produce sperm and the ovaries produce eggs. Sperm are very small and nucleated. It consists of head, midsection and movable tail. Eggs are large, round and have three polar bodies.
Function of reproductive cells: Sperm and egg participate in reproductive function.
7. Cnidocyte cell: Nidoblast cells are widespread everywhere except the soles of hydra. It is located in the spaces between the muscle cells. The cells look round, oval, flax-shaped, cupped or pear-shaped. Each cell is bilayered and contains only one nucleus. There are nematocysts with twisted threads inside the cells.
Nidoblast function
(i) It helps in food intake.
(ii) It helps in locomotion.
(iii) Participates in self-defence.
(iv) Captures and traps prey.
(v) Helps the animal to cling to an object.
(vi) It carries taxonomic importance.

Longitudinal or transverse section of Hydra showing the body wall and gastrovascular or coelenteron. The body wall consists of two cell layers. Epidermis (embryonic ectoderm) and gastrodermis (embryonic endoderm).
The outermost cell layer of the body wall is called the epidermis. The thickness of the epidermis is one-third that of the body wall. It contains seven types of cells. Muscle sheath cells, interstitial cells, sensory cells, nerve cells, glandular cells, germ cells and nidoblasts.
1. Musculo-Epithelial cells: Musculo-epithelial cells are located throughout the epidermis. The cells look columnar. The outside of each cell is wide and free and the inside is closed and narrow. There are two muscle enhancers on the inside. It is also called muscle tail. Within the muscle tail are the contractile fibers myoneme. The cytoplasm of the cell contains a nucleus, mucous material and granular glands. The cells lining the musculature are large, flattened and contain nidocytes. Mucin is secreted from the mucous material and granules from the granular glands. Muscle sheath cells are interconnected to form an integral sheath.
Musculoskeletal function
(i) Musculature protects the body by creating a body covering.
(ii) Myoneme causes contraction-expansion of the body.
(iii) Mucous gland secretion keeps the body slippery.
(iv) It bears nematocysts.
(v) It helps in movement by contraction-expansion.
(vi) Mucous granules secreting sap form the cuticle.
(vii) It contains nidoblasts.
(viii) Keeps the body attached to an object.
(ix) Part rich in mucous granules participates in digestion.
2. Interstitial cell: Interstitial cells are located in clusters between muscle cells. It is called Reserve cell or Stem cell or multipotent cell. The cells appear round, oval or triangular in shape. Each cell contains a nucleus, numerous mitochondria, endoplasmic reticulum, lysosomes, ribosomes etc. It has totipotency capability. So it transforms into any other cell as needed. The diameter of the cells is 5 μm.
Function of interstitial cells
(i) A cell can transform into any other cell.
(ii) It participates in hydra regeneration, growth, gonad and bud formation.
(iiii) After 45 days, when body cells are destroyed, interstitial cells fill the space.
3. Sensory cell: Sensory cells are scattered in the spaces between the muscle covering cells. However, it is numerous in karshika, hypostome, feet. The cells appear narrow, elongated and spindle-shaped. That is, the middle part is wide and both ends are narrow. Each cell has cytoplasm and a swollen nucleus. It has contractile membranes on the outside and sensory nerves on the inside. It is sensitive to light, heat, touch, chemicals etc. Dr. Siddiq Publications
Function of sensory cells
(i) It receives different types of stimuli from the environment.
(ii) It participates in self-defense.
(iii) It helps in selection of accommodation.
(iv) It selects food.
4. Nerve cells: Nerve cells are located under the epidermis near the mesoglia. The cells appear maculate or polygonal. Cytoplasm and nucleus are present in the cell. Each cell has two or more branched nervous systems. Nervous systems combine to form the neural network. Dr. Siddiq Publications
Nerve cell function
(i) It receives nerve impulses from sensory cells and generates reports.
(ii) It facilitates coordination between different cells.
5. Gland cell: Gland cells are located in the peduncle, hypostome and peduncle. Cells may appear cylindrical, granular, or oval. It contains mucous glands, enzyme glands and glands that secrete mucus.
Function of glandular cells
(i) A cell helps in digestion of food.
(ii) The secreted sticky juice keeps the hydra attached to an object.
(iii) It helps in locomotion by creating momentum.
(iv) Helps hydra to float in water by creating bubbles.
6. Germ cell: During the reproductive season, spermatozoa and ovum are formed from interstitial cells in the hydra body stem. The testes are above and the ovaries are below. The testicles produce sperm and the ovaries produce eggs. Sperm are very small and nucleated. It consists of head, midsection and movable tail. Eggs are large, round and have three polar bodies.
Function of reproductive cells: Sperm and egg participate in reproductive function.
7. Cnidocyte cell: Nidoblast cells are widespread everywhere except the soles of hydra. It is located in the spaces between the muscle cells. The cells look round, oval, flax-shaped, cupped or pear-shaped. Each cell is bilayered and contains only one nucleus. There are nematocysts with twisted threads inside the cells.
Nidoblast function
(i) It helps in food intake.
(ii) It helps in locomotion.
(iii) Participates in self-defence.
(iv) Captures and traps prey.
(v) Helps the animal to cling to an object.
(vi) It carries taxonomic importance.

Hydra is a small tube-shaped animal. When expanded they are about 1-3 cm long and 1 mm wide. When removed from the water, they turn into a soft and shapeless lump. Hydra’s body consists of three parts. Hypostome, body stem and foot.
1. Hypostome: The word Hypostome is formed from hypo meaning below and stoma meaning mouth. The upper part of the body has a mouth opening. The small and twisted contractile organ below the stoma is called the hypostome. Stomata receive food, water and oxygen. It expels undigested or waste material.
2. Body: The entire body except the hypostome and the base is called the body. Different parts of the body-
(i) Sterile: At the base of the hypostome there are 6-10 slender, long, hollow and contractile-expanding sturgeon. Each karshika is twice or thrice as long as the body. The outer wall of Karshika consists of batteries of small nematocysts like tumors. Karshikas are arranged in a circle. It participates in food intake, movement and self-defense.
(ii) Mukul: Favorable environment or environment with sufficient food during summer. Hydra gains physical growth by consuming food. As a result, one or more buds are formed in the middle region of the body. Each bud matures and gives birth to a new hydra. This is one of hydra’s asexual reproduction methods. Dr. Siddiq Publications
(iii) Genitalia: During hibernation and winter, temporary genitalia are formed on the body of the metamorphosed hydra. The upper part of the body contains the spermatozoa and the lower part the ovary. The testicles produce sperm and the ovaries produce eggs. Participates in sperm and egg production.
(iv) Pedicel: The part between the stem and the foot is the petiole. It is narrow, narrow and contractile. It connects the body and the foot.
3. Padachakti: The round and pressed part in the lower part of the body is the sole of the foot. A sticky substance secreted from the soles of the feet keeps the hydra attached to objects. Bubbles help float in water. It helps the hydra to move by forming a membrane. Hydra displays gliding movements with the help of discs. Dr. Siddiq Publications