Diversity in Living Organisms
Diversity in Living Organisms > Ask Alfie
Hi
Draw a neat labelled diagram of Hydra.
Structure of Hydra:
External Structure of Hydra: (i) Shape and Size: Hydra is a polypoid coelenterate with a cylindrical body. It is easily visible to the naked eyes and when fully extended, it becomes elongated and slender. It measures from 2 to 20 mm in length. This variation in the length is due to its remarkable power of contraction and expansion. (ii) Body Form: Hydra appears tubular. It is sessile but its proximal or aboral end is drawn out into a slender stalk at the end of which is the basal disc or pedal disc for attachment to the substratum. The pedal disc region of the body is provided with gland cells which secrete adhesive substance for attachment to the substratum and also a gas bubble fox floating. The free distal end or oral end of the body bears a conical elevation called hypostome. The hypostome bears an aperture at its apex called mouth which opens into the gastrovascular cavity or enteron. The hypostome is encircled by a circlet of 6-10 tentacles (L., tentare = to feel). The tentacles are hollow; their cavity is communicated to the gastrovascular cavity, slender, thread-like processes having nematocysts. The tentacles can be greatly extended at the time of feeding or locomotion. At the proximal end of the body, it may bear lateral projections called buds in various stages of development. A well developed bud bears its own mouth, hypostome and tentacles.
External Structure of Hydra: (i) Shape and Size: Hydra is a polypoid coelenterate with a cylindrical body. It is easily visible to the naked eyes and when fully extended, it becomes elongated and slender. It measures from 2 to 20 mm in length. This variation in the length is due to its remarkable power of contraction and expansion. (ii) Body Form: Hydra appears tubular. It is sessile but its proximal or aboral end is drawn out into a slender stalk at the end of which is the basal disc or pedal disc for attachment to the substratum. The pedal disc region of the body is provided with gland cells which secrete adhesive substance for attachment to the substratum and also a gas bubble fox floating. The free distal end or oral end of the body bears a conical elevation called hypostome. The hypostome bears an aperture at its apex called mouth which opens into the gastrovascular cavity or enteron. The hypostome is encircled by a circlet of 6-10 tentacles (L., tentare = to feel). The tentacles are hollow; their cavity is communicated to the gastrovascular cavity, slender, thread-like processes having nematocysts. The tentacles can be greatly extended at the time of feeding or locomotion. At the proximal end of the body, it may bear lateral projections called buds in various stages of development. A well developed bud bears its own mouth, hypostome and tentacles.
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