Cephalopods are the most highly developed type of soft-bodied. As a rule, representatives of this group live in marine waters and prefer a tropical or subtropical climate. Nevertheless, some species live in more moderate conditions, including the polar territories.
Class Cephalopods: body structure
The body of representatives of this group is characterized by bilateral symmetry and is clearly divided into two main parts - the head and trunk. During evolution, the mollusk leg turned into a funnel and tentacles located around it. As for the shell, in more developed species it is reduced and is located under the skin (and may be absent). Primitive representatives are characterized by a large outer shell with many individual chambers.
The skin that covers the body consists of one layer of the epithelium and the connective tissue layer. By the way, some species have chromophore pigment cells, due to which they can change the color of the body, becoming almost invisible against the background of the habitat.
On the abdominal side of the body there is a mantle cavity into which the ducts of the reproductive and excretory systems open , as well as the anus.
Cephalopods use a very interesting method of transportation. Strong muscle contractions push water from the mantle cavity into the external environment, creating a repulsive force.
Cephalopods: internal structure
Digestive system . Only all members of the class belong to the group of predators. The main prey are crustaceans, small fish and other mollusks. First, the animal captures its prey using tentacles. Interestingly, in some species, the salivary glands produce poison, which kills the captured animal. Further, the food lends itself to the action of powerful horny jaws, after which it enters the throat. The ducts of the salivary glands open in the pharyngeal cavity , which digest polysaccharides and protein components. On the esophagus, a food lump enters the stomach, where it can be influenced by liver and pancreatic enzymes. Digested food is pushed into the intestine, which ends in the anus.
By the way, some animals of this class have a special device - the so-called "ink bag", which contains dark matter. In case of danger, the secret from the bag is injected through the anus, which allows the clam to quickly disappear.
The respiratory system consists of well-formed gills that are located on the sides, in the mantle cavity. The excretion system consists of 2 to 4 kidneys.
The circulatory system is also well developed and consists of the heart, blood vessels and the so-called "gill hearts", the pulsation of which provides blood oxidation. Interestingly, hemocyanin, which contains copper, was found to be a respiratory pigment in some representatives. That's why the blood of the octopuses is blue.
It is worth noting that this particular class of animals has the most developed nervous system among all invertebrates. The head ganglia are covered with a kind of skull box. The sensory organs - eyes, mechanical sensitivity, smell - are very well developed.
Cephalopods: the most famous representatives of the class
Each cephalopod representative has its own unique characteristics, amazing adaptations to hunting and life in the depths of the sea.
For example, cuttlefish spend almost all their time buried in the sand at the bottom of the reservoir. Only eyes are left open - this helps to quickly detect prey.
Octopus is another famous cephalopod, which prefers to live on a rocky bottom. Here he can perfectly disguise himself and hide next to the stone. The animal’s leg is divided into several tentacles with suction cups on the inside.
Another well-known group is squids, which today are considered the fastest and most active representatives of the class.