Page 163 - Atlas Of The World's Strangest Animals

COMPASS JELLYFISH 163

After anchoring themselves to a well-secluded piece of rock, Over time, the scyphistoma produce tiny jellyfish,just
the larvae develop into scyphistoma,which have tentacles for 5mm (0.2in) in diameter, and these quickly develop into
catching food. mature jellyfish.

they’re helpless creatures, flung from coast to coast by Comparisons
ocean currents.When they need to, they can swim by
contracting and relaxing their bell in a series of rhythmic In these images, compass and lion’s mane jellyfish (Cyanea capillata)
pulses, which pushes water out and propels them forwards. may look similar but, in real life, lion’s manes are giants! In northern
But, they’re usually found floating free in the upper layers oceans they can grow to about 50cm (19.7in) in diameter, with
of coastal waters, where food is plentiful and all they have tentacles up to 30m (98.4ft).The largest-ever recorded specimen had
to do is wait for it brush past. a bell of 2.3m (7.5ft) and tentacles of 36.5m (119.7ft) long!
Compass jellyfish eat small fish, crustaceans and
plankton and they do this using specialized stinging
organs called nematocysts, which line the jellies’ bell and
their 24 marginal tentacles. Each nematocyst contains a
Compass jellyfish
coiled, threadlike tube lined with barbed spines. Inside
these small ‘capsules’, the osmotic pressure (the difference
between the pressure inside and out) is extremely high.
When one of the jellyfishes’ tentacles touches prey, the
nematocyst is activated.Water rushes into the capsule,
which increases hydrostatic pressure (the pressure exerted
by a fluid).This, in turn, expels the barbed thread, like a
harpoon being shot from a gun.The spine penetrates the
prey’s skin, injecting it with paralyzing poison.
Using this amazing system, small creatures can be
caught and pulled into the mouth of the compass with
little danger of their struggles damaging the delicate
structure of the jelly’s body. Nematocysts work equally
well in defence too, giving would-be predators a stinging
Lion’s mane jellyfish
jolt.Although compass jellyfish aren’t as poisonous as
other species, their barbs are still extremely painful to
people. Even a dead compass jellyfish, washed up on the
shore, should be avoided because it is still capable of
inflicting a painful sting.

(c) 2011 Marshall Cavendish. All Rights Reserved.