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GENERAL CARACTERISTICS


The Cnidarios, also calls Coelenterates, are animals with RADIAL SYMMETRY that is to say, that its body can be divided, by means of different planes, in equal parts.

Cnidarians are characterized by the presence of stinging cells called cnidocytes that are used for the capture of prey and defense.

Most species are marine as jellyfish, Portuguese man-of-war, coral, sea anemone, and sea fans, but hydras are freshwater forms.
radial symmetry of a cnidarian

Radial symmetry

 

 

ORGANIZATION


Two body types are seen in cnidarians;

POLYP and MEDUSA

The polyp is a sessile, cylindrical form in which the oral end (mouth and tentacles) is directed upward and the aboral end is attached to the substrate. The polyp form is seen in hydras and sea anemones.

The form polyp is the asexual phase and lives fixed to the bottom. They have coat form in whose superior part the mouth is opened, that also does the times of anus, and that is surrounded by tentacles to pull in water and capture food

Corals, hydra and sea anemones exist in the polyp form as adults
form polyp

Sea anemone (form polyp)
   

The medusa body type (seen in a typical jellyfish) consists of a free-swimming, bell-shaped form with the aboral end directed upward and the oral end directed downward.

Jellyfish & Portuguese man-of-war are medusa form as adults

Some cnidarians are dimorphic or go through both polyp and medusa stages in their life cycle. However, all the cnidarios do not have both forms.

medusa form

Medusa form (jellyfish)

 

All cnidarians are carnivorous. Both, polyp and medusa, contain stinging cells called cnidocytes in their tentacles that contain coiled stingers called nematocysts that can shoot out and paralyze prey

¡¡Warning!!

It does not suit to take cnidarios without protection (gloves)
stinging cells (nematocysts)


Stinging cells (Nematocysts)

SEE ANIMATION

 

 

REPRODUCTION


Cnidarians have both sexual and asexual reproduction cycles.

Asexual reproduction occurs to form a new colony which may stay attached to the parent organism or break off to form a new one.

Medusa are the sexual stage

Most cnidarians have separate sexes.

Cnidarians (like sponges) also have tremendous regenerative powers so that broken parts form new organisms.

SEE ANIMATION

 

 

CLASSIFICATION


The Phylum Cnidaria contains about 10,000 species

There are three main Classes of Cnidaria
  Life cycle usually includes both polyp and medusa
Class HYDROZOA
  
  The medusa is the dominant form
Class ESCIPHOZOA
  
  All have the polyp body form
Class ANTHOZOA
  

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