Jellyfish, or sea jellies, have traditionally been considered simple and primitive.
When you gaze at one in an aquarium
tank, it’s not hard to see why. Like its relatives, the sea anemones and corals,
jellyfish looks like a no-frills animal.
The ancestors of jellies go back to a time before animals evolved
what we call bilateral symmetry – mirrored right and left sides –
or cephalization – the centralization of a brain and sensors, often
on a neck, and away from the main body. As a result, jellies,
anemones and corals have no head and no brain, no front or
back, no left or right; and while they have no legs, they often
have lots of arms, arranged in a circle around a central mouth.
While not the best arrangement for bounding across open fields
or swinging from the treetops, jelly architecture has been wildly
successful in the word’s oceans for nearly 600 million years. Now
That’s not to say that jellies haven’t changed in all that time. In
fact, jellies are one of the most diverse groups on the planet.
Some are nearly microscopic, while others can be the size of a
laundry basket, trailing thirty feet of stinging tentacles. Many are
transparent, some are luminous, while others, like the sea wasp
of Australia, are some of the deadliest animals in the sea.
Mostly marine, but also in fresh water,
jellies occupy 99.9% of the available living
space on Earth, from tropical lakes
and shallow lagoons to the deepest
ocean basins. If nothing else, these simple,
gelatinous organisms are some of
the most interesting animals on Earth.