Jellyfish don't have specialized digestive, osmoregulatory,
central nervous, respiratory, or cuirculatory systems. They digest
using thegastrodermal lining of the gastrovascular cavity, where
nutrients are absorbed. They do not need a respiratory system since
their skin is thin enough that the body is oxygenated by diffusion.
They have limited control over movement, but can use their
hydrostatic skeleton accomplish movement through
contraction-pulsations of the bell-like body; some species actively
swim most of the time, while others are passive much of the time.
Jellyfish are composed of more than 90% water; most of their
umbrella mass is a gelatinous material - the jelly - called
mesoglea which is surrounded by two layers of epithelial cells
which form the exumbrella (top surface) and subumbrella (bottom
surface) of the bell, or body....
