June, 2000 
25 
Hydroid colony (enlarged) 
pull back its tentacles and conlraci 
inio a little lump. 
Hydras feed on fresh water 
plankton animals. They catch their 
prey with the stinging capsules and 
thread capsules in their tentacles. 
Hydras can glide from place to place, 
and also move by turning over and 
over. 
Other Hydroids 
On the coral reef, many living things 
live on top of other living things. 
Look closely at a blade of sea grass, 
a bunch of seaweed, or a mass of 
coral. You may see a delicate white 
growth, like a tiny branching plant. 
It is one of the hydroid. a colony of I 
animals, related to Velella. 
There are many polyps living 
together in each little hydroid. The 
polyps feed on plankton, tiny living 
things that float in the sea. A hydroid 
colony grows by budding new polyps. 
At certain times, the hydroid also 
forms reproductive polyps. They 
produce tiny jellyfish-like medusae 
Some of the small medusae are 
males, and others arc females. They 
shed their eggs and sperms into the sea. 
A sperm fertilises an egg. and the egg 
grows into a larva. The larva swims 
for a while, then settles down on a 
surface. It becomes attached, develops 
tentacles, and buds off new polyps to 
form a hydroid colony. 
SEA ANEMONES 
Sea Anemones are animals that look 
like flowers. They live in the sea, all 
over the world. 
At low tide along rocky shores, 
look in cracks, or hollows called 
tidepools Small green anemones like 
little flowers often live along cracks 
in rocks, or the edge of tidepools. You 
may even find a small pink anemone 
growing on the shell of a crab or 
mollusc! 
Sea anemones have a tube-shaped 
body. It is soft but tough. like rubber. 
The sea anemone clings to a surface at 
one end. On the other end is an opening 
called a mouth. 
A sea anemone’s mouth is 
surrounded by a ring of tentacles. The 
tentacles have stinging capsules and 
sticky thread capsules to stun and 
entangle small fish and other prey. 
When they sense danger, sea anemones 
can pull their tentacles back inside their 
bodies. 
