Shellfish (also called soft-bodied) are a huge variety of living organisms. They are distributed throughout the earth since ancient times. Even in the Cambrian period, they appeared on the planet and since then 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 figure out one important aspect of their life. How is regeneration developed in mollusks? What does biology say about this? More details below. Why are mollusks poorly developed regeneration? So, let's begin.
Class mollusks. general characteristics
Strictly speaking, mollusks are a type composed of several classes. The body of the mollusk does not consist of segments. As a rule, the structure of these animals secrete the head, body and leg. For mollusks, the presence of a mantle is characteristic - folds of the body that forms the mantle cavity, which communicates with the external environment. For many of them, a shell is characteristic (bivalve, spiral or in the form of a rudiment).
The brightest representatives of the class:
- Gastropods Representatives: grape snail, ampoule, achatine.
- Bivalve mollusks (having lost their heads during evolution). Representatives: oyster, mussel, toothless.
- Cephalopods (transforming their foot into tentacles). Representatives: octopus, squid, cuttlefish.
The general concept of the property of regeneration in the animal world
To understand why regeneration is poorly developed in mollusks, we need to understand what this concept means. This property is more or less characteristic of each representative of the living world. Change of leaves on trees, skin renewal in humans, molting of animals are all examples of regenerative processes. Another thing is that the ability to it is different for each species and class. Consider only the animal kingdom (for plants: subject to 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 a complication of the structure of the animal, we observe a decrease in the ability to regenerate. So, a person cannot grow a lost limb, in contrast to, for example, tailed amphibian newts. But the pond frog, also related to amphibians, is not able to grow a new paw instead of the lost one. Its regeneration is only enough to tighten the wound formed by the connective tissue and grow its skin, which in itself is also regeneration, although much weaker than that of the newt. From each segment of a flat parasitic worm - a bovine tapeworm - a separate individual can grow. Round or annelids are much less capable of regeneration. The reproduction of starfish in aquariums occurs by dividing them into individual rays. Each of them is able to form a separate organism.
Features of mollusks and their regeneration
From the above it follows that the property of regeneration does not manifest itself equally in different classes of living beings. Let us find out whether regeneration in mollusks is strongly or poorly developed, and why. Of course, from a small part of the body a full-fledged mollusk cannot be grown. Mollusks are very highly organized (for example, the squid eye is not inferior in complexity to the eyes of mammals, although the vision systems have developed in us and they independently). The non-segmented body structure is also characteristic of creatures with weak regeneration. But we must not forget that all animals are capable of regeneration, at least to a small degree: after all, the mollusks have epidermal cells renewed, hemolymph cells renewed. Grater cells on the tongue of the snails are updated, the shell grows, increasing in size, which means that new body cells gradually replace old ones that have outlived or supplement them, allowing the mollusk to grow.
Regeneration Examples
Regeneration in various representatives of this class occurs 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 regeneration property is expressed, perhaps most strongly from mollusks. So, his cut off tentacle is soon replaced by a newly regrown one. Squids also have a chopped-off tentacle replaced with 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 motor squid. The gastropod mollusks cannot boast of such successes in terms of regeneration of lost organs. But the eye instead of the remote is quite capable of growing.
Thus, we found out why regeneration is poorly developed in mollusks. Firstly, 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. potential for self-reproduction). Finally, one cannot say that the whole type is characterized by an equally low ability to regenerate. This type is extensive, and within the classes included in its composition, this property manifests itself in different ways.