White planaria is a representative of flat ciliary worms, which are characterized by a more complex development than coelenterates. Let's get acquainted with the description of the appearance, internal structure, and lifestyle features of this small animal.
Description
The white planarian worm, as its name implies, is distinguished by its milky-white translucent body, on which black round eyes clearly stand out. Features of the appearance of the animal are as follows:
- Elongated body no more than 2 cm long, less than 5 mm thick. It has mirror symmetry.
- Noticeable flattening in the back.
- The front part, on which the organs of touch are located, is expanded. The back is slightly pointed.
Outside, the body of the white planaria is covered with cilia, between which there are tubular glands that secrete mucus. It is used when animals move in the water column, and is also thrown out in case of danger. On the head are twogrowths on which the eyes are located. The internal structure of these representatives of the fauna is still primitive in many respects, but it is already an order of magnitude higher than the coelenterates.
Specific structure
Type of worms white planaria refers to multicellular complex organisms. Like other flatworms, it has a three-layer structure. A brief description of each of the layers is presented in the form of a table.
| Layer | Characteristic |
| Ectoderm | Outer layer of skin |
| Mesoderm | Middle layer, for internal organs acts as protection and support |
| Entoderm | Inner layer fused with muscles |
Each of these three layers is formed in planarian embryos.
Like other flatworms, the body of the white planaria is formed by several tissues:
- Nervous.
- Muscular.
- Connective.
- Integumentary.
Outside, the body of the animal is covered with a layer of cilia, thanks to which the planaria is able to move.
Note that the following components are missing in the internal structure of this flatworm:
- Brain.
- Circulatory system.
- Anal hole.
They also don't have a body cavity.
Skin-muscle bag
The muscles of the planarian, covering its entire body, are formed by the fusion of the mesoderm andectoderm, consists of muscle fibers, several muscle groups are distinguished in its structure:
- Ring. Located across the body under the cilia. With their contractions, they are able to stretch and narrow the body.
- Slanting. Located under the circular muscles.
- Longitudinal. This is the lower layer of muscles, the purpose of which is to unite the dorsal and abdominal regions of the body.
- Spinal-abdominal bundles.
Due to such a complex system of muscles, the white planaria has the ability to make various movements, envelop objects of the outside world. The skin-muscular sac also performs a respiratory function, since the flatworm does not have special respiratory organs. Under the muscles is the parenchyma - a loose cell mass, in which the primitive organs of the animal are located.
Organ systems
Let's continue to consider the features of the internal structure of the white planaria. Of particular interest is the digestive system of the ciliary worm, which has a closed character:
- There is a mouth opening on the belly, which is why the animal needs to be above it to capture food.
- The movable pharynx, whose main functions are sucking out soft tissues and then swallowing food, is pushed out of the mouth opening with the help of contracting muscles.
- Further, food enters the midgut, which is a direct continuation of the pharynx, where it is digested with the help of digestive juices, which are secreted by the glandular cells of the intestine. Thanks to the complex devicethe central part of the midgut of a planarian can absorb various foods, including large ones. Here, food digested to a molecular state is absorbed into the cells. The intestine ends with the caecum.
- Because the animal does not have an anus, food debris is expelled through the mouth.
This is how planarians digest.
The excretory system can be conditionally divided into two parts:
- Digestive organs.
- Skin consisting of tubular holes that release carbon dioxide and suck in oxygen.
Through special tubules located on the skin, harmful substances and excess fluid are removed from the body.
The animal also has a rather primitive nervous system, in which several organs are distinguished:
- Two longitudinal nerve columns.
- Ganglion.
- Inter-barrel cross bridges.
- A lot of small nerves.
The peculiarity of this flatworm is that the organs of the nervous system are concentrated in the head.
Due to the presence of nerve cells, the white planaria has sensitivity, touch, and reacts to external stimuli (exposure to electric current, bright lighting). The outgrowths-tentacles located on the head are very sensitive, thanks to them the animal is able to recognize the source of the threat or food. Also, this ciliary worm is characterized by a primitive vestibular apparatus.
Distribution
Whiteplanaria is a representative of the fauna that is widespread on planet Earth, most often this ciliary worm lives under small pebbles or on a muddy bottom in freshwater reservoirs.
He feels comfortable in aquariums, causing real horror among fish lovers, as he begins to actively hunt for small representatives of the fauna - crustaceans and shrimps.
Sometimes planarians become parasites, choosing to live in the shell of a representative of crustaceans. A single worm is not terrible for a larger aquatic inhabitant, but when their number increases and they penetrate the gills, the "carrier" may even die.
Lifestyle features
Having examined the structure of the white planaria, we learn how it lives. This living being moves by means of muscle contractions. Under adverse conditions, the planaria is able to divide its body into parts, each of which becomes a separate individual capable of reproduction under normal conditions. Most often, this division occurs with a lack of oxygen or elevated temperatures. This phenomenon in science is called autotomy.
The amazing abilities of planarians interested scientists from different countries. Such an experiment is known: several individuals, through prolonged training, learned to go through a certain labyrinth. Then they were destroyed, ground and fed in this form to other planarians who had never been in the labyrinth. Surprisingly, these animals managed to find a way out on the first try, as if they had gained knowledge and experience as a result of digestiveprocess.
Planarians have practically no natural enemies, because due to the specific taste of bitter mucus, these flatworms are unattractive to fish.
Food
White planaria is heterotrophic in terms of nutrition, because, like all animals, this worm does not have the ability to synthesize organic matter, but is a small predator, partly a saprophyte, eating carrion, the remains of food that has been digested by larger aquatic inhabitants. An animal's "favorite treats" include:
- Shrimp.
- Fish caviar.
- Crustacean eggs.
- Worms are even smaller than herself.
In captivity (for example, in laboratory research), planarians are often fed white bread. For full development, the animal needs protein, therefore, it chooses the appropriate food for itself.
Specific asexual reproduction
Since the white planarian is a hermaphrodite (that is, it has both male and female genital organs in its body), both sexual and asexual reproduction are possible for it. In the second case, the mother individual is divided into two parts across the body, each of the "halves" regenerates (restores) to the state of a full-fledged individual. Most often, ciliary worms use such reproduction in an unfavorable environment.
Sexual reproduction
The reproductive system in flatworms is present and consists of the following parts:
- The female organs of the white planaria are the ovaries and oviduct.
- Male testes and ductus.
Sexual reproduction is a complex process that includes several steps:
- Copulation of individuals (in the scientific literature it is called copulation), while due to the specific location of the genital organs, contact occurs on the ventral sides.
- The sperm of one of the individuals enters the copulatory pouch of the second, moves along the oviducts and enters the seminiferous receptacles.
- During the fusion of male and female germ cells, a zygote is formed.
- The fertilized zygote moves through the oviducts, being covered with a membrane due to cell nutrients.
- Zygote, covered with a dense shell, is an egg the size of a pinhead, which is attached to the leaves of aquatic flora with the help of special stems. Sometimes planarians hide their eggs behind rocks.
After 15-20 days, young flatworms appear from the eggs, which gradually become adults. The life cycle of this animal is in many ways unique to flatworms.
Interesting facts
After considering the lifestyle of the white planaria, we learn some interesting facts about this animal:
- These little worms are able to distinguish between up and down.
- In case of danger, the planarian secretes a special mucus, very bitter and slippery, which is poisonous to small animals.
- For a complete regeneration of the body, it is enough to save even though30%, while the organism will be identical, having the same properties and characteristics as the original individual.
- If a planaria reproduces by division, then each of the individuals will give out the same reactions to external stimuli as the mother. During sexual reproduction, each new individual independently forms reactions.
White planarians, despite their primitive structure, are very interesting creatures, although representatives of the scientific world are primarily concerned about their ability to regenerate. They are completely harmless to humans, but can be chosen as an object of observation.
