June, JCOO 
23 
stage. and many jellyfish 
do iioi have a polvp 
stage 
JELLYFISH 
Two-thirds ot ihe Earth's 
surface is covered by 
oceans, and all over the 
oceans there are 
jellyfish A jellyfish is 
usually shaped like a 
bell, or an overturned 
bowl. Between the outer 
and inner layers of cells there may be 
a layer of thick, clear jelly The 
jellyfish's mouth is inside the 'bell* 
Jellyfish swim by contracting and 
relaxing their bodies, or they simply 
float Jellyfish feed on small animals 
in the open sea They catch their prey 
with stinging capsules. A few jellyfish 
have tiny algae in the tissues around 
their mouth They tloai upside-down, 
so the algae get plenty of sunlight to 
make food. 
Moon jellyfish 
producing) Scientists place Comb 
Jellies m a separate group, the 
Phylum Ctenophora 
HYDROZOANS 
These cmdarians all have stinging 
capsules, which they use for feeding 
and defense Most hydrozoans arc 
colonial many individuals living 
together, and acting like one organism. 
Moon jellyfish Aurelia aurita 
Moon jellyfish are tound in all seas 
They are about the size and shape of 
an orange cut in half, hut clear and 
almost colourless From a boat, you 
may see thousands of moon jellyfish 
drifting with the currents near the 
surface of the sea. 
Note: The Comb Jellies are small, 
delicate transparent animals They 
are abundant in the ocean , from the 
surface to great depths Many of 
them are luminescent ( light - 
By-the-wind-Sailor Velella velella 
After a storm, the beach may be 
littered with violet discs about the size 
of a shilling. On each disc is a small 
stiff sail that seems to be made of 
plastic. These discs arc the bodies of. 
the bv the-wind-sailor. Millions of 
Velella float on the surface of warm 
seas. They are blown about by the wind 
on their stift clear sails. They catch 
tiny plankton for food. Plankton is 
composed of many small living things 
lloating near the surface of the sea. 
A Velella is actually a group of 
