No head

Radial symmetry

Humans have a bilateral symmetry, while the moon jellyfish has a radial symmetry.

Cnidarians have no head and are sac formed with a mouth in one end. They are also radially symmetrical. This implies that they are like a cake that can be divided into three equal parts. The human body illustrates those animals that are symmetrical bilaterally, they can only be divided into two equal parts.
    Cnidarians do not possess anything that can be called a brain. This implies that they are insensitive and devoid of the power of decision. Nerve impulses are transplanted through the body like ripples on water.
    Cnidarians are devoid of well developed sensory organs. There are very few that can see and probably none that can hear. Moon jellyfish can however experience their surroundings with several senses.
    The cnidarian group incorporates about 270 specie in Swedish waters and about 9 000 specie globally. Often they are sub-divided into several groups, the hydrozoas, the jellyfish and the anthozoas.
    Read about the different cnidarians!!

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson