Mollusks (also called soft-bodied) are a huge variety of living organisms. They have been distributed throughout the earth since ancient times. Even in the Cambrian period, they appeared on the planet and since then they have mastered all the seas and continents: mollusks live in the air, on land, in water, and even in other organisms as parasites. Let's try to understand one important aspect of their life. How do molluscs develop regeneration? What does biology say about this? More details below. Why do molluscs have poorly developed regeneration? So let's get started.
Clam class. General characteristics
Strictly speaking, molluscs are a phylum consisting of several classes. The body of molluscs does not consist of segments. As a rule, in the structure of these animals, the head, body and leg are distinguished. Mollusks are characterized by the presence of a mantle - a fold of the body that forms a mantle cavity, which communicates with the external environment. Many of them are characterized by a shell (bivalve, spiral or rudimentary).
The brightest representatives of the class:
- Gastropods. Representatives: grape snail, ampoule,Achatina.
- Bivalve molluscs (which have lost their heads in the process of evolution). Representatives: oyster, mussel, toothless.
- Cephalopods (transforming their legs into tentacles). Representatives: octopus, squid, cuttlefish.
General concept of the property of regeneration in the animal world
To understand why regeneration is poorly developed in molluscs, we need to understand what this concept means. This property is to some extent characteristic of each representative of the living world. The change of leaves on trees, the renewal of human skin, the molting of animals are all examples of regenerative processes. Another thing is that the ability to it in each species and class is different. Consider only the animal world (for plants: under optimal environmental conditions and hormonal levels, a whole plant can be obtained from any cell, this property of cells is called totipotency). As a rule, with the complication of the structure of the animal, we observe a decrease in the ability to regenerate. So, a person cannot grow back a lost limb, unlike, for example, tailed amphibian newts. But the pond frog, also related to amphibians, is not able to grow a new leg to replace the lost one. Its regeneration is only enough to tighten the resulting wound with connective tissue and overgrow it with skin, which in itself is also regeneration, although much weaker than that of a newt. From each segment of a flat parasitic worm - a bull tapeworm - it can grow in a separate individual. Roundworms or annelidsmuch less capable of regeneration. Reproduction of starfish in aquariums occurs due to their division into separate rays. Each of them is able to form a separate organism.
Peculiarities of shellfish and their regeneration
From the above, it follows that the property of regeneration does not manifest itself in the same way in different classes of living beings. Let us find out whether regeneration is strongly or poorly developed in mollusks, and why. Of course, a full-fledged mollusk cannot be grown from a small part of the body. Mollusks are very highly organized (for example, the eye of a squid is not inferior in complexity to the eyes of mammals, although our and their vision systems developed independently). An unsegmented body structure is also characteristic of creatures with poor regeneration. But we must not forget that all animals are capable of regeneration, at least to a small extent: after all, in all mollusks, epidermal cells are renewed, hemolymph cells are renewed. The grater cells on the tongue of snails are renewed, the shell grows, increasing in size, which means that new body cells gradually replace obsolete old ones or supplement them, allowing the mollusk to grow.
Examples of regeneration
Regeneration occurs in different representatives of this class to varying degrees, depending on their biology. How regeneration is developed in some species of mollusks, we will consider in further examples. In octopuses, the property of regeneration is expressed, perhaps most strongly among molluscs. So, his cut off tentacle is soon replaced by a regrown one. Squid also cut offthe tentacle is replaced by a new one - all thanks to the fact that each of the three pairs of tentacles is served by a separate heart. These three hearts support the autonomy of the squid's motor divisions. Gastropods cannot boast of such success in terms of regeneration of lost organs. But instead of the removed eye, they are quite capable of growing back.
Thus, we found out why mollusks have poorly developed regeneration. First, their body is not divided into segments. Secondly, they are very difficult to organize. Thirdly, it is a property of their cells and tissues; low totipotency (i.e., the potential for self-reproduction). Finally, it cannot be said that the entire type is characterized by an equally low ability to regenerate. This type is extensive, and within the classes that make up it, this property manifests itself in different ways.
