Cnidarians (coming from the Greek CNIDOS= stinging needle) are incredibly diverse in form but come in two fundamental shapes, polypoid and medusoid shapes.  The main characteristic feature is the presence tentacles set in a radial symmetry with their digestive system in the middle.  On these tentacles are found the nematocysts (stinging cells that can be ejected at a prey if they come close enough) used to subdue and capture food by the use of a toxin, that can be sometimes even lethal to man.  Cnidarians can be found as single element or in colonies (like coral) 

There are 9000 species (400 in the Mediterranean) of cnidarians organized in four major groups: Anthozoa, which includes true corals, anemones, and sea pens; Cubozoa, the amazing box jellies with complex eyes and potent toxins; Hydrozoa, the most diverse group with siphonophores, hydroids, fire corals, and many medusae; and Scyphozoa, the true jellyfish.

Anthozoa

• Asteroides Clycularis

• Calliactis Parasitica

• Alicia Mirabilis

• Condy Lactis Aurantiaca

Hydrozoa :

• Velella Vellella