Hydras: Hydras is a genus of tiny fresh-water organisms that are classified under the phylum of Cnidaria. Hydra has a cylindrical, radially symmetric body from 2 to 20 mm in length. It is visible to the naked eyes when fully extended. Typically, hydras remain attached to some underwater objects, waving their tentacles slowly with the current. This is why the hydra is often mistaken for a plant or alga. However, it is a bona fide animal.

Classification of Hydras

• Kingdom: Animalia – Hydras belongs to kingdom Animalia (metazoa). As such, they are multicellular eukaryotic organisms that depend on other organisms as their source of food.
• Phylum: Cnidaria – Hydras belongs to the phylum Cnidaria. This phylum is also composed of such polyps as sea anemones medusae and corals. This group of organisms has the following characteristics: they are aquatic, they have tentacles, they have a single body opening they have two body layers and are, for the most part, radially/biradially symmetrical.
• Class: Hydrozoa – Class Hydrozoa is composed of tiny predatory organisms that may live in colonies or as solitary animals. A majority are found in marine environments while a few live in freshwater. Hydrozoa is characterized by an internal digestion space, presence of an exoskeleton, two body forms as well as the presence of cnidocytes
• Order: Hydroida – The order Hydroida is composed of hydroids that are characterized by three basic stages of life, a tubular body, two body layers that mostly use asexual reproduction.
• Genus: Hydras – (below are characteristics of the genus Hydra).

Structure of Hydras

• A hydras body is structured in the shape of a tube with tentacles grouped around its head pole. A closer look shows a mouth, a peduncle, and a basal disc, which the organism uses to connect to the substrate.
• These polyps range in size from 1 to 2 cm in height, with tentacles varying in length based on the species. The tentacles of a green Hydra, for example, can be as long as 5 cm when they’re relaxed and as long as 20 cm when expanded.
• Buds sprouting out from the parent organism may be seen on the hydra’s exterior surface. Hydra has a core cavity called the coelenteron that serves as the gastrovascular cavity on the inside.
• The testis containing sperm cells and the ovary carrying the egg are reproductive structures found under the ectoderm in hydra.
• Hydra, being diploblastic creatures, have 2 kinds of tissue layers: ectoderm and endoderm, which constitute the internal gastrodermis and outer epidermis, respectively, divided by the mesoglea.

Reproduction in Hydras

Asexual Reproduction in Hydra

• Budding is the method through which hydra reproduce asexually. This is Hydra’s most frequent way of reproduction, which happens in the presence of optimal environmental circumstances.
• Through the recurrent process of mitosis of the epidermis interstitial cells, a tiny bud grows near the parent Hydra’s basal portion during budding. Cell differentiation leads to the creation of the coelenteron, the oral portion, and the tentacles as mitotic division proceeds.
• It restricts as the base and eventually splits to become an autonomous creature once completely formed. From start to finish, this process might take up to three days.

Sexual Reproduction in Hydra

• Unlike asexual reproduction, reproduction in Hydra which is sexual happens when the organism’s environment becomes unfavourable.
• Temperature changes, particularly cold temperatures and a lack of suitable food sources induce the organism to begin forming gonads to prepare for sexual reproduction. As a consequence, reproduction in Hydra, like that of many other marines and freshwater creatures, is restricted to specific times.
• Gonads emerge from the interstitial epidermis and create a bulge on the hydra’s body wall in anticipation of sexual reproduction.
• Ovaries, like testes, are generated by the growth of interstitial cells. The growth of Oocyte, which grows in size and produces a big nucleus follows – one ovary can have 1 or 2 two ovum.

The fertilized egg undergoes a number of steps that include:

• Cleavage – The process that produces blastomeres – cells of equal size.
• Blastulation – Results in the production of the blastula with a narrow cavity (blastocoel).
• Gastrulation – The blastula starts reorganizing into a multilayer structure known as the gastrula.
• Encystation – A cyst forms around the embryo allowing the embryo to survive changes in the environment. Here, the embryo remains dormant until environmental conditions improve.
• Hatching – When environmental conditions improve, the embryo develops further by increasing in size and developing tentacles. This phase is also characterized by the rapture of the cyst. The new offspring then continues growing until it matures.

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By Team Learning Mantras