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Australia: The Land Where Time Began |
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Jellyfish Anatomy Stinging Cells and Sticky Cells
The organisms of the Cnidaria and Ctenophora, the 2 main phyla
containing jellyfish, the structures used to capture food and in defence
are completely different from each other. In the Cnidaria stinging
cells, cellular organelles, known as nematocysts, are used, while
ctenophores use colloblasts, in food capturing and defence.
Nematocysts stinging cells
All cnidarians possess nematocysts (stinging cells), their phylum name
Cnidaria came from the Greek word for nettle. The possession of
nematocysts is the primary characteristic that unites such disparate
organisms as stony corals, soft corals, sea anemones, sea pansies, sea
fans, hydra, medusan jellyfish, and siphonophores.
Each nematocyst is essentially a keratinised capsule with double walls
with a coiled up harpoon inside and a trapdoor with a hair Trigger at
one end. Even slight mechanical stimulation may cause the harpoon to
discharge because of the hair trigger. The harpoon is discharged with an
explosive power of 40,000 Gs (40,000 times the force of gravity) which
makes the discharging nematocyst one of the fastest biological
processes. Eversion, or turning inside out, is the mechanism by which
the nematocyst discharges. The harpoon shaft is hollow and often has
perforations. As the harpoon penetrates the skin it may deliver venom in
3 different ways: by hypodermic injection through the tip of the
harpoon, through the perforations along the shaft of the harpoon and by
the residue on the outside of the shaft. These 3 delivery mechanisms
result from the venom being contained in the capsule, inside the harpoon
as well as on its outer surface. There are strong spines on the shaft of
the harpoon, particularly near its base, that help anchor the harpoon in
the prey as it penetrates. There may be 3 rows of smaller spines on the
remainder of the shaft, or possibly none at all.
Colloblasts sticky cells
Colloblasts that are present in ctenophores have no harpoon, being more
similar to a rope covered in an adhesive substance. There is no venom in
colloblasts, and they are only used in the capture of food, not in
defence.
The colloblast consists of a bouquet-shaped structure, a collosphere,
which has adhesive granules, and is supported by an axial (central)
thread around which is wrapped a spiral filament. When the colloblast is
stimulated the spiral thread straightens, which activates the
colloblast, the granules bursting to release their glue. There are large
numbers of colloblasts on tentacles and lobes present on Ctenophores,
and present on the fine tentacles around the lips of some species.
Haeckelia rubra is one
species that completely lacks colloblasts, though it co-opts nematocysts
for its own protection from the jellyfish it preys upon.
Jellyfish stings
Nematocysts have received a lot of attention from researchers because of
their venom, but not so much research has been carried out on
colloblasts. It has been found that generally different areas of
jellyfish have different types of nematocysts, such as the bell,
tentacles, lips and stomach. Many dozens of different types of
nematocysts have been identified. Typically the structures discovered
have been spherical, ovoid, lemon-shaped and banana-shaped. For many
cnidarian groups the identification of species is helped by the number
and forms of nematophytes that are present. They are often the only
means by which a species can be distinguished from another species,
especially after stings, fragments of tentacles or nematocysts remaining
on the skin may be the only objective evidence that is available.
There is a very simple method for retrieving nematocysts from the skin
following a sting: adhesive tape is placed on dry skin area sticky side
down and pressed to the skin and peeled up. The tape is then examined
under a microscope. This provides a method of identifying the species of
jellyfish responsible for the sting that is non-invasive, safe and
effective.
The treatment for a jellyfish sting is largely species specific.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |