Ciliary worm, or turbellaria (Turbellaria) belongs to the animal kingdom , a type of flatworm, numbering more than 3,500 species. Most of them are free-living, but some species are parasites that live in the host's body. The sizes of individuals fluctuate depending on the habitat and feeding habits. Some worms can only be examined under a microscope, while others reach a length of more than 40 cm.
Parasites are almost all representatives of the type of flatworms. Ciliary worms are the only class that includes forms that freely inhabit the environment, but are predators.
Worms can be found in salt and fresh water, in moist soil, under stones, along the banks of rivers and lakes. Some live on the surface of the earth, others below it. Small 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 planaria, which come in all kinds of colors (from black and white to brown and blue).
Description of the appearance of the ciliary worm
The class of ciliary worms is so named 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 and a mouth located in front of the peritoneal part of the body.
Features of the ciliary cover
Ciliary epithelium is of two types:
- with clearly separated cilia;
- with merged cilia in one cytoplasmic layer.
Not all members of the flatworm class possess cilia. Ciliary types of worms under the epithelial layer hide secretion glands. The mucus secreted from the front of the body helps the worm attach and hold onto the surface of the substrate, as well as move without losing balance.
On the edges of the worm's body are unicellular 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 eventually grow bald, losing particles of the epithelium, which resembles molting in animals.
The structure of the skin and muscle bag
The structure of ciliary worms is similar to the structure of all flatworms. The muscular organ forms a skin-muscle bag and consists of three layers of fibers:
- an annular layer located externally on the surface of the body;
- a diagonal layer whose fibers are at an angle;
- longitudinal bottom layer.
When contracting, the muscles provide rapid movement and sliding of especially large individuals.
Digestive system
Some representatives of ciliary worms do not have a clearly defined intestine and are intestinal. In others, the digestive organs are represented by a whole system of branching 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 the intestinal (genus convolute), ciliary worms are divided:
- rectal (mesostomy);
- enteric (milk planaria, trilacid).
The mouth of individuals with a branching intestine is located closer to the back of the body, in the rectal - 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 of ciliary worms has pharyngeal glands responsible for the external (outside the body) digestion of food.
Highlight system
The excretory system is represented by a multitude of pores in the posterior part of the animal’s body, through which unnecessary substances are ejected through special channels. Small channels are connected to one or two main channels adjacent to the intestine.
In the absence of the intestines, secretions (excreta) accumulate at the surface of the skin in special cells, which, after filling, disappear safely.
Nervous system
Characterization 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 a large number of neural branches.
The sensory organs are developed, special motionless cilia are responsible for the tactile function. Some individuals have a developed sense of balance, for which a special organ of the statocyst, represented in the form of subcutaneous vesicles or pits, is responsible.
The perception of movements and irritating actions from the outside occurs through sensilla - immobilized cilia over the entire surface of the body.
In worms with the presence of a statocyst, an orthogon connected to it forms a lattice-type system of brain channels.
Developed sense of smell and vision
The ciliary worm has olfactory organs, which play an important role in his life as a predator. It is thanks to them that turbellaria find food. On the sides of the rear and front ends of the body are pits, which 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 an assumption that some especially large terrestrial species are able to visually distinguish objects, they have a shaped lens. Although the eyes, and in most cases several dozen paired and unpaired eyes, are located near the worm in the region of the brain ganglia on the front surface of the body.
The light that enters the visual sensitive retinal cells in the concave parts of the eyes provokes the generation of a signal that is delivered to the brain for analysis through nerve endings. Retinal cells are akin 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 - to breathe. Indeed, most flatworms are anaerobes, that is, organisms living in an oxygen-free environment.
Breathing is vital and occurs through the entire surface of the body, which absorbs oxygen directly from the water through many microscopic pores.
Corm Worm Nutrition
Most of these animals are predators and many of them have an external digestive system. Attaching the mouth to a potential victim, the worm secrets a special secret produced by the pharyngeal glands, which digests food from the outside. After this, the worm sucks nutrient juices. This phenomenon is called external digestion.
The type of flatworm class cilia feeds mainly on small crustaceans and other invertebrates. Unable to swallow and bite through the shell of large crustaceans, the worms secrete a special mucus filled with enzymes inside. It softens the victim, practically digesting it, and then the worm simply sucks out the contents of the shell.
The presence of teeth in the worms replaces the throat, with the help of which they swallow the whole food. If the victim is large, then the worm with abrupt sucking movements of the mouth tears off a small piece from it, gradually absorbing all the prey.
Breeding
The class of ciliary worms is represented by hermaphrodites, which have both male and female sex glands. Male cells are in the testes. Special seed canals depart from them, delivering sperm to the meeting place with the eggs.
The female genital organs are represented by the ovaries, from which the eggs are sent to the oviducts, then to the vagina, and then to the resulting genital cloaca.
Genital fertilization occurs by cross. The worms fertilize each other alternately, alternately injecting sperm through the copulate organ resembling the penis into the opening of the genital cesspool.
The seminal fluid fertilizes the eggs and an egg is formed, covered by a shell. Eggs emerge from the body of the worm, from which an individual hatches, in appearance it already looks like an adult worm.
Only in turbellaria (type flatworms, class ciliary), an microscopic larva similar to an adult appears from an egg, which floats with cilia along with plankton until it grows up and transforms into an adult 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 regenerative ability
Some representatives of ciliary worms, for example, planaria, are able to repair damaged parts of the body again. Even pieces of the body the size of a hundredth of an entire individual can re-grow into a new full-fledged worm.
The planaria from the three-branched order thus learned to survive in adverse environmental conditions. With a significant increase in water temperature, with a lack of oxygen, the worms spontaneously break up into pieces in order to recover again by regeneration when the external conditions return to normal.
Planaria ciliary worm is the largest representative of the class that lives in water bodies. The predator feeds on small invertebrate animals. Worms themselves do not become food for fish due to the presence of glands that secrete toxic substances.
Parasites
Parasitic ciliary worms include:
- Dark cephalus that live on the skin of freshwater invertebrates and turtles, laying eggs on the surface of the host body. Dark cephalus is small (up to 15 mm), their body is flat, there are several tentacles. The ciliary worm is a hermaphrodite and lives mainly in the southern hemisphere.
- Udonellids - formerly referred to flukes, but now they are isolated in a detachment of ciliary worms. They have a cylinder-shaped body and a small size (up to 3 mm). Using a suction cup, they attach to crustaceans, which, in turn, parasitize on the gills of large marine fish.
Some types of turbellaria live only in the waters of Lake Baikal, due to the uniqueness of its waters. Most ciliary worms not only do no harm, but are also an integral part of their habitat. Destroying small mollusks, they control a population of invertebrate animals, preventing it from growing to incredible sizes.