White Planaria: type of worms, structure, lifestyle

White planaria is a representative of flat ciliary worms, which are characterized by a more complex development than intestinal. Let's get acquainted with the description of the appearance, internal structure, lifestyle features of this small animal.

Description

The worm is a white planaria, as its name implies, has a milky white translucent body, on which black round eyes stand out clearly. Features of the appearance of the animal are as follows:

• The elongated body is not more than 2 cm in length, 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 are placed tubular glands that secrete mucus. It is used when moving animals in the water column, and is also thrown out in case of danger. On the head are two growths on which the eyes are located. The internal structure of these representatives of the fauna is still largely primitive, but it is already an order of magnitude higher than the intestinal.

The specifics of the structure

The type of worms white planaria belongs to multicellular complex organisms. Like other flatworms, it has a three-layer structure. A brief description of each of the layers is presented in table form.

Each of these three layers is formed in planarium embryos.

Like other flatworms, the body of the white planaria is formed by several tissues:

• Nervous.
• Muscular
• Connective.
• The coverslip.

Outside, the animal’s body is covered by a layer of cilia, thanks to which the planaria is able to move.

Note that in the internal structure of this flatworm, the following components are missing:

• Brain.
• Circulatory system.
• Anal opening.

They also have no body cavities.

Muscular skin bag

The muscles of the planaria, covering its entire body, are formed by the fusion of the mesoderm and ectoderm, 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. They are located under the ring muscles.
• Longitudinal. This is the lower layer of muscles, the purpose of which is to combine the dorsal and abdominal areas 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 from the outside world. The skin-muscle bag 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

We continue to consider the features of the internal structure of the white planarium. Of particular interest is the digestive system of the ciliary worm, which is closed in nature:

• There is a mouth opening on the belly, which is why an animal needs to be above it to capture food.
• The mobile pharynx, the main functions of which is the suction of soft tissues and subsequent ingestion of food, is pushed out of the mouth with the help of contracting muscles.
• Next, the food enters the middle intestine, 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. Due to the complex arrangement of the central part of the middle intestine, the planaria can assimilate various foods, including large ones. Here, food digested to a molecular state is absorbed into the cells. The intestine ends with the cecum.
• Since the animal does not have an anus, food debris is removed through the mouth.

This is the digestion process of planarians.

In the excretory system, two parts can be conditionally distinguished:

• Digestive organs.
• The skin consists of tubular openings that emit carbon dioxide and absorb oxygen.

Through special tubules located on the skin, harmful substances and excess fluid are eliminated from the body.

The animal also has a fairly primitive nervous system, in which several organs are secreted:

• Two longitudinal nerve columns.
• Ganglion.
• Crossbar cross jumpers.
• A large number of small nerves.

The peculiarity of this flat worm 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, reacts to external stimuli (exposure to electric current, bright lighting). The tentacle outgrowths located on the head are very sensitive, thanks to them the animal is able to recognize the source of the threat or food. Also for this ciliary worm is a primitive vestibular apparatus.

Spread

The white planetarium 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 bodies of water.

He feels comfortable in aquariums, causing genuine horror among fish lovers, as he begins to actively hunt for small representatives of the fauna - crustaceans and shrimps.

Sometimes planaria become parasites, having chosen a shell of a representative of crustaceans as a shelter. A single worm is not afraid of a larger water 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 planarium, we learn how it lives. This living creature moves through muscle contractions. Under adverse conditions, a 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 the planarians interested scientists from different countries. Such an experiment is known: several individuals learned to go through a maze through long trainings. Then they were destroyed, grinded and fed in this form to other planarians that had never been in the maze. Surprisingly, these animals managed to find a way out on the first attempt, as if having gained knowledge and experience as a result of the digestive process.

Planaria has virtually no natural enemies, because of the specific taste of bitter mucus, these flatworms are unattractive to fish.

Nutrition

The white planarium is heterotroph in type of nutrition, because, like all animals, this worm does not have the ability to synthesize organic matter, but is a small predator, partially saprophyte, eating carrion, the remnants of food that was digested by larger aquatic inhabitants. Among the "favorite treats" of the animal are:

• Crustaceans.
• Fish roe.
• Crustacean eggs.
• Worms are even smaller than herself.

In captivity (for example, when researching in the laboratory), the planaria is often fed with white bread. For full development, the animal needs protein, so it chooses the appropriate food for itself.

The specifics of asexual reproduction

Since the white planaria is a hermaphrodite (that is, in her body there are both male and female genital organs), then sexual and asexual reproduction is possible for her. In the second case, the maternal 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 this 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 the oviduct.
• Male testes and vas deferens.

Sexual reproduction is a complex process, includes several stages:

• The copulation of individuals (in the scientific literature is called copulation), while due to the specific location of the genitals, the contact occurs on the ventral sides.
• The sperm of one of the individuals falls into the cumulative bag of the second, moves along the oviducts and enters the testicles.
• During the fusion of male and female germ cells, a zygote is formed.
• The fertilized zygote moves along the oviducts, becoming covered by the membrane due to the nutrients of the cells.
• The zygote, covered with a dense shell, is an egg the size of a pinhead, which is attached to the leaves of the aquatic flora with the help of special stems. Sometimes planarians hide eggs behind stones.

After 15-20 days, young flatworms appear from the eggs, which gradually become adults. The development cycle of this animal is largely unique to flatworms.

Interesting Facts

Having examined the lifestyle of the white planarium, we find out some interesting facts about this animal:

• These small worms are able to distinguish between top and bottom.
• In case of danger, the planaria emits a special mucus, very bitter and slippery, which is poisonous to small-sized animals.
• For complete regeneration of the body, it is enough that at least 30% is retained, while the body will be identical, possessing the same properties and characteristics as the original individual.
• If the planaria reproduces by division, then each of the individuals will produce the same reactions to external stimuli as the mother. During sexual reproduction, each new individual independently forms a reaction.

The white planarians, despite the primitive structure, are very interesting creatures, although representatives of the scientific world care primarily about their ability to regenerate. They are completely harmless to humans, but can be chosen as an object of observation.