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 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 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.
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.
A. The octopus bends its body by contracting either one of the two longitudinal muscles, which enables it swim in the water.
1. Longitudinal Muscles
B. 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
4. Circular Muscles
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.
1. Water intake
Shown in the figure are the jet propulsion cycle and sections of the cuttlefish. The cycle begins with enlargement (A). 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 (B). 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 (C). 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.
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.
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
"…The kingdom of the heavens and the earth and everything between them belongs to Allah. He creates whatever He wills. Allah has power over all things."
The reactive swimming systems, ink discharge-based defensive methods, the acute vision and the colour changing skin abilities that cuttlefish have are perfect examples of creation.
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.
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.
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.
"And in your creation and all the creatures
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.