Jellyfish have two major body forms throughout their life.
The first form is called the polyp stage and is characterized
by either a non-moving (sessile) stalk that catches food
drifting by or a similar form that is free-floating. Their
mouth and tentacles are located anteriorly, facing upwards.
The second form looks like a saucer is called the medusa
stage and is characterized by a round (radially symmetric)
dome-shape body plan with food catching tentacles hanging
down. It is this form which is most able to respond to
and interact with its environment and is also the form
most people are familiar with. With few exceptions, jellies
are dioecious, which means that each animal is either
male or female. A group of animals releases sperm and
eggs which may mix in the water column and become fertilized
or, in the case of the moon jelly (Aurelia), the eggs
become lodged in pits on the oral arms, which form a temporary
brood chamber where fertilization takes place.
|
