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Medusa Necklace in 925 Silver and Blue Opal Stone

Medusa Necklace in 925 Silver and Blue Opal Stone

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Medusa Necklace in 925 Silver and Blue Opal Stone

Jellyfish (Class Scyphozoa) belong to the large group of cnidarians (Phylum Cnidaria), together with sea anemones and corals . Their body is characterized by a radial symmetry and develops concentrically around a central axis: turning around a jellyfish we will in fact always see it the same, regardless of the angle from which we observe it!
The shape of these animals is unmistakable: their body (called umbrella ) resembles a bell, from whose lower edge dozens of tentacles branch off, facing downwards. On the concave side of the organism, in a central position, there is a cylindrical-shaped structure called the dumbbell, at the end of which there is the mouth. This is the only opening in the animal and opens into a blind cavity called the gastrovascular cavity.

Jellyfish are very simple organisms and their bodies only consist of three layers:

  • the epidermis, the outermost layer, which acts as a barrier to the surrounding environment;
  • the gastrodermis, the innermost layer, which lines the gastrovascular cavity;
  • and finally the mesoglea, a gelatinous mass that is interposed between the other two layers and which favors the floatation of the animal. The English name of jellyfish derives from the mesoglea, which gives the jellyfish the characteristic jelly-like appearance .

Tentacles and nutrition: a pungent beauty

What makes jellyfish so unpleasant to swimmers all over the world are their stinging tentacles : in fact, unlike the umbrella, they are able to cause annoying wounds. How? Thanks to the presence of hundreds of specialized cells to capture prey (cnidocytes).

Each cnidocyte contains within it a microscopic capsule ( nematocyst ) which in turn contains a spiral wound filament capable of injecting venom into the prey or enveloping it. The mechanism that activates these highly effective weapons is of a mechanical type: it is enough that the prey (or the unfortunate bather) touches a tentacle to trigger the nematocysts. Although their ability to move is very limited, thanks to this sophisticated system, jellyfish are able to prey on organisms that are much more complex and faster than them.

Reproduction: the octopus-jellyfish cycle

The life cycle of jellyfish varies from species to species and can be more or less complex and include different stages. In general, two phases are identified, which follow one another in the life of an animal in the so-called polyp-jellyfish cycle:

  1. OCTOPUS PHASE: benthic form, lives adhering to the substrate. It has a tubular body, with
    mouth and tentacles pointing upwards. It reproduces asexually by budding, splitting
    or laceration of the foot.
  2. PHASE OF MEDUSA: freely floating, lives in the water column. The body is shaped like a
    bell with mouth and tentacles pointing downwards. The jellyfish represents the form
    “Adult” of the cycle and reproduces sexually by producing eggs and spermatozoa, from which
    fusion originate the polyps.

Curiosities about jellyfish

Despite being very simple organisms, jellyfish can reach considerable size! This is the case of the lion's mane jellyfish (Cyanea capillata), whose umbrella can reach 2 m in diameter and whose tentacles can measure up to 35 m!

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