Invertebrates’ Amazing Swimming and Defense Systems

By A. O.


The cuttlefish can avoid its predators through very swift movements as a result of these fast muscular contractions.

Invertebrates’ Amazing Swimming and Defense 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 maneuver 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 backward.

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 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 synthesized 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.

InvertebratesThe cuttlefish is not the only animal swimming by means of a reactive system. Octopuses also utilize 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.

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 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.


A Note by the Editor:

Allah the Almighty says in the Ever-Glorious Qur’an what means,

“He [Allah] hath created the heavens without supports that ye can see and hath cast into the earth firm hills so that it quake not with you, and He hath dispersed therein all kinds of beasts. And We send down water from the sky and We cause (plants) of every goodly kind to grow therein. This is the Creation of Allah. Now show me that which those (ye worship) beside Him have created. Nay, but the wrongdoers are in error manifest!” (Luqman 31: 10-11)


“We shall show them Our portents on the horizons and within themselves until it will be manifest unto them that it is the Truth. Doth not thy Lord suffice since He is Witness over all things? How! Are they still in doubt about the meeting with their Lord? Lo! Is not He surrounding all things?” (Fussilat 41: 53-54)


A. O. is a Turkish writer and author.


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