Ciliary worm, or turbellaria (Turbellaria) belongs to the animal kingdom, a type of flatworm, with more than 3,500 species. Most of them are free-living, but some species are parasites that live in the body of the host. The sizes of individuals fluctuate depending on the habitat and feeding habits. Some worms can only be seen under a microscope, others reach a length of more than 40 cm.
Parasites are almost all flatworms. Ciliary worms are the only class that includes forms that live freely in the environment, but are predators.
Worms can be found in s alt and fresh water bodies, in moist soil, under stones, along the banks of rivers and lakes. Some live on the surface of the earth, others below it. Few species live on the surface of the host's body, being parasites, but not causing him much harm. The most numerous and spectacular representatives of the class are planarians, which come in all sorts of colors (from black and white to brown and blue).
Description of the appearance of the eyelash worm
The class of ciliary worms is named so because the entire body of the worm is covered with small cilia, which ensure the movement of the animal and the movement of small individuals in space. Ciliary worms move by swimming or crawling, like a snake. The body shape of animals is flattened, oval or slightly elongated.
Like all representatives of flatworms, their body does not have an internal cavity. These are bilaterally symmetrical organisms, with sensory organs located in front and a mouth on the peritoneal part of the body.
Features of the eyelash cover
Ciliary epithelium is of two types:
- with clearly separated eyelashes;
- with fused cilia into one cytoplasmic layer.
Not all flatworms have cilia. Ciliary worm species hide secretion glands under the epithelial layer. The mucus secreted from the front of the body helps the worm attach and stay on the surface of the substrate, as well as move without losing balance.
On the edges of the worm's body are single-celled glands that secrete mucus with toxic properties. This mucus is a kind of protection of the animal from other larger predators (for example, fish).
Ciliary worms seem to grow bald over time, losing particles of the epithelium, which resembles molting in animals.
The structure of the skin-muscular sac
The structure of ciliary worms is similar to the structure of all flatworms. The muscular organ forms a skin-muscular sac and consists of three layers of fibers:
- annular layer located outside on the surface of the body;
- diagonal layer whose fibers are at an angle;
- longitudinal bottom layer.
By contracting, muscles provide fast movement and gliding of especially large individuals.
Digestive system
Some representatives of ciliary worms do not have a clearly defined intestine and are intestinalless. In others, the digestive organs are represented by a whole system of branched channels that deliver nutrients to all parts of the body. It is the structure of the intestine that distinguishes the orders of ciliary worms. In addition to intestinalless (a kind of convolut), they share ciliary worms:
- rectal (mesostomy);
- veterinary (milk planaria, tricladids).
The mouth of individuals with a branched intestine is located closer to the back of the body, in rectal ones - to the front. The mouth of the worm is connected to the pharynx, which gradually passes into the blind branches of the intestine.
The class Ciliary worms have pharyngeal glands responsible for external (outside the body) digestion of food.
Isolation system
The excretory system is represented by many pores on the back of the animal's body, through which unnecessary substances are ejected through special channels. Small channels are connected toone or two main, adjacent to the intestines.
In the absence of the intestines, secretions (excretions) accumulate near the surface of the skin in special cells, which, after filling, safely disappear.
Nervous system
The characteristic of ciliary worms includes differences in the structure of the nervous system. In some types, it is represented by a small network of nerve endings (ganglia) in the front of the body.
Others have up to 8 paired nerve trunks with many neural ramifications.
The sense organs are developed, special fixed cilia are responsible for the tactile function. Some individuals have a developed sense of balance, for which a special statocyst organ is responsible, presented in the form of subcutaneous vesicles or pits.
The perception of movements and irritating actions from the outside occurs through sensilla - immobilized cilia over the entire surface of the body.
Worms with the presence of a statocyst form an orthogon connected to it - a lattice-type system of brain canals.
Developed sense of smell and vision
The eyelash worm has olfactory organs, which play an important role in its life as a predator. It is thanks to them that turbellarians find food. On the sides of the rear and front ends of the body there are pits that are responsible for the transfer of signals and molecules of smelling substances from the outside to the brain organ.
Worms do not have vision, although there is speculation that some especially largeterrestrial species are able to visually distinguish objects, they have a formed lens. Although the eyes, and in most cases several dozen paired and unpaired eyes, are located in the worm in the region of the brain ganglia on the front surface of the body.
Light falling on the visual sensitive retinal cells in the concave areas of the eyes provokes the production of a signal that is delivered to the brain for analysis through nerve endings. Retinal cells are similar to the optic nerve, which transmits information to the brain ganglia.
Animal breath
The characteristic of the class of ciliary worms differs from the type of flatworms in that free-living individuals are able to absorb oxygen - breathe. After all, most flatworms are anaerobes, that is, organisms living in an oxygen-free environment.
Respiration is vital and occurs through the entire surface of the body, which absorbs oxygen directly from the water through many microscopic pores.
Ciliary worm nutrition
Most of these animals are carnivores and many of them have an external digestive system. Attached by the mouth to a potential victim, the worm secretes a special secret produced by the pharyngeal glands, which digests food from the outside. After that, the worm sucks out the nutritious juices. This phenomenon is called external digestion.
The type of flatworms that feed on ciliary class are mainly small crustaceans and other invertebrates. Unable to swallow and bite throughthe shell of a large crustacean, the worms secrete inside a special mucus filled with enzymes. It softens the victim, almost digesting it, and then the worm simply sucks out the contents of the shell.
The presence of teeth in worms replaces the pharynx, with which they swallow food whole. If the victim is large, then the worm tears off a small piece from it with sharp sucking movements of the mouth, gradually absorbing all the prey.
Reproduction
The class of ciliary worms is represented by hermaphrodites, having both male and female gonads. The male cells are found in the testicles. Special seminal ducts depart from them, delivering sperm to the meeting point with eggs.
The female reproductive organs are represented by the ovaries, from which the eggs are sent to the oviducts, then to the vagina, and then to the formed genital cloaca.
Sexual fertilization occurs in a cross way. The worms alternately fertilize each other, alternately injecting sperm through the penis-like copulatory organ into the opening of the genital cloaca.
The seminal fluid fertilizes the eggs and an egg is formed, covered with a shell. Eggs come out of the worm's body, from which an individual hatches, already similar in appearance to an adult worm.
Only in turbellaria (a type of flatworm, the ciliary class), a microscopic larva similar to an adult emerges from the egg, which swims with the help of cilia along with plankton until it grows up and transforms intoadult worm.
These worms can also reproduce asexually. At the same time, a constriction appears on the body of the worm, which gradually divides it into two equal parts. Each part becomes a separate individual, which grows the organs necessary for life.
Amazing ability to regenerate
Some representatives of ciliary worms, such as planarians, are able to regenerate damaged areas of the body. Even pieces of the body the size of a hundredth of a whole individual can re-grow into a new full-fledged worm.
Three-branched planaria thus learned to survive in unfavorable environmental conditions. With a significant increase in water temperature, with a lack of oxygen, the worms spontaneously break into pieces in order to recover again by regeneration when external conditions return to normal.
The planarian ciliary worm is the largest representative of the class that lives in water bodies. The predator feeds on small invertebrates. The worms themselves do not become food for fish due to the presence of glands that secrete toxic substances.
Parasite
Ciliary parasitic worms include:
- Temnocefalians that live on the skin of freshwater invertebrates and turtles, laying eggs on the surface of the body of the host. Dark-cephalians are small in size (up to 15 mm), their body is flat, there are several tentacles. The eyelash worm is a hermaphrodite and lives mainly in the southern hemisphere.
- Udonellids - formerlyrelated to flukes, but now they are separated into a detachment of ciliary worms. They have a cylindrical body and a small size (up to 3 mm). With the help of suckers, they attach themselves to crustaceans, which, in turn, parasitize the gills of large marine fish.
Some species of turbellaria live only in the waters of Lake Baikal, due to the uniqueness of its waters. Most eyelash worms are not only harmless, but are an integral part of their habitat. By destroying small mollusks, they keep the population of invertebrates under control, preventing it from growing to incredible sizes.
