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Reactive Swimming
Systems
Vertebrates are the fastest running, best swimming and
farthest flying creatures on earth. The main factor underlying all
of these abilities is the presence of skeletons made of hard materials
such as the bones that do not lose their shape. These bones provide
tremendous support for contracting and flexing muscles, which bring
about continuous movements through moving joints.
However, invertebrates move at much lower speeds, in
comparison with vertebrates, due to their boneless structures.
 Cuttlefish
receive great help during hunting from the tentacles in its
mouth. These whiplike tentacles normally remain coiled in
pouches beneath its arms. When the fish encounters a prey,
it unleashes them and snatches up the prey. The fish relies
on its adequately designed arms (eight in total) to take care
of the rest. It can easily tear a crab to bits by using its
beak. The cuttlefish uses its beak with such mastery that
it can neatly puncture the shell of a crab and rasp out the
meat with its tongue.36 |
Cuttlefish are invertebrates that do not have bones in
their bodies despite being called fish. They have extraordinary
abilities to manoeuvre because of a very interesting system. Their
soft body is covered with a thick mantle under which large amounts
of water are drawn and flushed out by strong muscles and that enables
them to escape backwards.
This mechanism in cuttlefish is highly complex. On both
sides of the animal's head are pocket-like openings. The water is
drawn in through these openings into a cylinder-shaped cavity inside
its body. Then, it jets out this water from a narrow pipe immediately
under its head with great pressure, which enables it to move swiftly
in the opposite direction due to reactive forces.
This swimming technique is highly appropriate in terms
of both speed and durability. A Japanese cuttlefish, called Todarodes
Pacificus, in their migration of 1250 miles (2000 kilometres) travel
at about 1.3 mph (2 km/h). For short distances, it can accelerate
up to 7 mph (11 km/h). Some species are known to exceed 19 mph (30
km/h).
The cuttlefish whose
scientific nomenclature is Loligo Vulgaris are the smallest
among their species. Their reactive swimming system enables
them to move at speeds in excess of nineteen mph (30 km/h).
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The cuttlefish can avoid its predators through very swift
movements as a result of these fast muscular contractions. When
their speed alone is not enough for safety, they squirt a cloud
of dense, dark coloured ink that is synthesised in their bodies.
This ink surprises their predators for a few seconds, which is usually
enough for them to escape. The undetectable fish behind the ink
cloud leaves the area immediately.
The defence system and reactive swimming styles of cuttlefish
also work for them during hunting. They can attack and chase their
prey at high speeds. Their immensely complicated nervous system
regulates the contractions and flexing necessary for their reactive
swimming. Accordingly, their respiratory systems are also in ideal
condition, which provides the high metabolism that is needed for
the jet propulsion.
The cuttlefish is not the only animal swimming by means
of a reactive system. Octopuses also utilise this system. However
they are not active swimmers; they spend most of their time wandering
over rocks and gorges in the deep sea.
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The cuttlefish also has radial and circular
muscles as in the octopus, but instead of the octopus' longitudinal
muscles there is a fibrous layer in the cuttlefish. This layer
prevents its body from elongation when both the muscles contract
as well as providing a sturdy base for the radial muscles.
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The octopus bends
its body by contracting either one of the two longitudinal
muscles, which enables it swim in the water.
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The inner skin of the octopus is composed of many layers
of muscles one on top of another. They constitute three different
types of muscles called longitudinal, circular and radial. These
structures enable various movements of the octopus by balancing
and supporting one another.
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Shown in the figure are the
jet propulsion cycle and sections of the cuttlefish. The cycle
begins with enlargement (1). The outside diameter of the body
is enlarged by 10% of the normal size, which increases the
volume of the mantle cavity by about 22%. Water enters from
the openings on both sides of the head passing through the
funnel-shaped pipe. When the maximum enlargement is reached,
the diameter of the body is reduced to 75% of normal size
(2). Pressure in the cavity suddenly increases and pushes
the inner tap on the mouth of flushing-out pipe, which closes
the water intake. Nearly all the water (approximately 60%
of normal body size) is forcefully expelled out through the
pipe. The body recovers its normal shape by the intake of
water (3). Any further contractions could easily harm the
creature. The jet propulsion lasts about one second and can
be repeated 6 to 10 times in a row, including suction time.
When swimming slowly the body of the cuttlefish contracts
to 90% of its original size.
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When flushing water out, the circular muscles contract
lengthwise. However, since they have the tendency to maintain their
volume, their width increases, which would normally elongate the
body. In the meantime, the stretching longitudinal muscles prevent
the elongation. The radial muscles remain stretched during these
happenings that cause the mantle to thicken. After the jet propulsion,
the radial muscles contract and shrink the length, which causes
the mantle to become thinner, and the mantle cavity to be filled
with water again.
The eye structure of a cuttlefish is extremely
complex. It can focus the pupil by bringing the lens nearer
to the retina. It can also adjust the volume of light taken
into the eye by closing or opening the little lids beside
the eye. The presence of such highly complex organs in structures
of two completely distinct species such as humans and cuttlefish
cannot possibly be explained by evolution. Darwin also spoke
about this impossibility in his book.38
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The muscular system in the cuttlefish closely resembles
that of the octopus. However, there is an important difference:
the cuttlefish has a layer of tendons, called the tunic, instead
of the longitudinal muscles of an octopus. The tunic is composed
of two layers that cover the inside and outside of the body just
like the longitudinal muscles. In between these layers are the circular
muscles. The radial muscles are situated in between these, in a
perpendicular orientation.
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Under the skin of the
cuttlefish is arrayed a dense layer of elastic pigment sacs
called chromatophores. By using this layer, they can change
the apparent colour of their skin, which not only helps in
camouflage but also acts as a way to communicate. For instance,
a male fish can take on a different colour when mating than
that it would take on when in a fight with a challenger.
When a male flirts with a female,
it takes on a bluish colour. If another male comes by during
this, it gives a reddish colour to the half that faces the
other male. Red is the warning colour used during a challenge
or an aggressive action.
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A thin layer of skin
that surrounds the arms and the body further supports the
reactive swimming system of the cuttlefish. The fish floats
in the water by means of waving this curtain-like membrane.
The arms, on the other hand, function to balance the body
during the floating. They also work for braking during stopping.
The reactive swimming systems
of the octopus and the cuttlefish actually function according
to a principle that resembles jet planes. Through a closer
examination, it is obvious that their muscular systems have
been designed in the way most suited to them. It is, of course,
absurd to assert that such complex structures could have been
formed through coincidences.
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"And in your creation and
all the creatures He has spread about there are Signs for
people with certainty."
(Surat al-Jathiya: 4)
There is
an equally flawless design in the reproductive systems of
cuttlefish. The eggs of these fish have sticky surfaces that
enable them to adhere to cavities in the deeps of the sea.
The embryo consumes the nutrients provided inside the egg
until it is ready to hatch. The embryo breaks the egg casing
with a small brushlike patch on its tail. This feature disappears
shortly after hatching.39 Every little detail
has been designed and functions as it is designed to do. All
of this miraculous creation is nothing but an expression of
the infinite knowledge of Allah.
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36. Fred Bavendam, "Chameleon
of The Reef", National Geographic, September 1995, p. 100.
37. Stuart Blackman, "Synchronised Swimming", BBC
Wildlife, February 1998, page 57.
38. Charles Darwin, The Origin of Species, The Modern
Library, New York, pp. 124-153.
39. Fred Bavendam, "Chameleon of The Reef", National
Geographic, page 106. |
