|
Return to front page
|
|
Feeding & venom
Box jellyfish feed on fish, crustaceans and other marine invertebrates.
They use potent venom to quickly kill their prey so that it does
not escape. The venom is contained in stinging cells called nematocysts.
Most box jellyfish have several different types of nematocysts;
the type and proportion of nematocysts can be used to identify some
species.
 |
Stinging cells have miniature harpoons coiled inside them.
Photo by Teresa Carette, JCU. |
The stinging cells have a miniature harpoon coiled inside them which
is everted (turned ‘inside –out’) when the jellyfish
contacts its prey. The bulb of the nematocyst injects toxin through
the shaft and into the prey. The tentacle is contracted, and the
pedalia (structures at the base of the tentacles near the bell)
push the food into the manubrium or mouth which is located inside
the bell. Once the nematocysts are fired, the jellyfish has to produce
new nematocysts to replace them.
Chironex fleckeri has tentacles that can be extended to
more than three metres long. There are billions of nematocysts along
each tentacle. When Chironex fleckeri are young and are
eating mostly prawns, only five percent of their nematocysts contain
venom which is potent to vertebrates. However, as they grow and
their diet switches to fish, the proportion of vertebrate-potent
venom increases and can be found in 30-40 percent of the nematocysts.
It takes only a few centimetres of Chironex tentacle to
kill a small fish. Only a few metres of tentacle (which may contain
billions of stinging cells) is needed to contact a swimmer’s
exposed flesh to deliver a dose of venom that could be fatal within
minutes. Species of box jellyfish that cause ‘Irukandji syndrome’
appear to feed mainly on larval or adult fish.
|
