Jellyfish

Jellyfish

Jellyfish are free-swimming marine animals, a species of Cnidaria, the most ancient group of Eumetazoans.

Biology

Keywords

jellyfish, Cnidaria, Cnidocyte, rocket principle, gastric cavity, tentacles, epitheliomuscular cell, marine, predator, floating lifestyle, alternation of generations, animal, living organism, biology

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Scenes

  • - It contains neurons and epitheliomuscular cells. Neurons form a diffuse nervous system: nerve cells are distributed throughout the organism, without advanced nerve centers, though there may be ganglia. The bodies of epitheliomuscular cells form the epidermis, but they are also responsible for the movement of the jellyfish.

  • - There is no separate epidermal and muscle tissue in Cnidaria. The bodies of epitheliomuscular cells form the epidermis and they are also responsible for the movement of the jellyfish. Their elongated base contains contractile protein fibers to provide mobility for the jellyfish.
  • - It causes to epitheliomuscular cells to contract by electric signals. They form a diffuse nervous system: nerve cells are distributed throughout the organism, without advanced nerve centers, though there may be ganglia.

  • - It contains neurons and epitheliomuscular cells. Neurons form a diffuse nervous system: nerve cells are distributed throughout the organism, without advanced nerve centers, though there may be ganglia. The bodies of epitheliomuscular cells form the epidermis, but they are also responsible for the movement of the jellyfish.
  • - There is no separate epidermal and muscle tissue in Cnidaria. The bodies of epitheliomuscular cells form the epidermis and they are also responsible for the movement of the jellyfish. Their elongated base contains contractile protein fibers to provide mobility for the jellyfish.
  • - It causes to epitheliomuscular cells to contract by electric signals. They form a diffuse nervous system: nerve cells are distributed throughout the organism, without advanced nerve centers, though there may be ganglia.

Narration

The life cycle of Cnidarians usually involves an alternation of generations, in which a polyp generation alternates with a medusa generation. Polyps, usually sessile, produce motile medusas through asexual budding. The medusas are free swimming predators; they produce a new generation of polyps through sexual reproduction. Medusa-form Cnidarian individuals are called jellyfish.

During their embryonic development, Cnidarians form two germ layers: an outer core, called the endoderm, and an inner one, called the ectoderm. That is, they do not yet exhibit a middle germ layer, or mesoderm. The two germ layers develop into the outer and the inner body layers, that is, the epidermis and the gastrodermis. These layers are connected by a jelly-like middle layer, called mesogloea.

The inner layer contains gland cells which secrete digestive enzymes that start the digestion process. Digestive cells absorb the partly digested materials and complete their digestion. That is, in Cnidaria both intracellular and extracellular digestion are present.
The epidermis contains epitheliomuscular cells. The elongated base of these cells contains contractile protein fibers that provide mobility for the jellyfish. Neurons regulate the contraction of the epitheliomuscular cells with electric signals.
The neurons form a diffuse nervous system: nerve cells are distributed throughout the organism, without advanced nerve centers, through which they may be ganglia. Cnidocytes contain a toxin that is fired into the prey.

As soon as the prey touches the ciliary receptors of the cnidocyte, it is activated, thus the hinged operculum opens, the cnidocil penetrates the body surface of the prey, and the fired thread injects venom into the wound. This process takes place in less than a microsecond.

The oral arms contain the highest number of cnidocytes. The jellyfish uses its oral arms to direct its prey into the gastric cavity.

Jellyfish may also pose a threat to humans. The most dangerous jellyfish is the box jellyfish, which is estimated to be responsible for the death of around a hundred people every year.

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