Interesting features are characteristic of a group of multicellular animals, which are of the type Sharpening, or Cnidaria. Cnidarians have a simple structure, but they have real tissues, an intestinal cavity. One of the unofficial names of the group is intestinal. An important role in the body is played by stinging cells (cnidocytes, nematocytes). They serve to attack prey and defend against enemies.
What organisms have knidocytes?
Stalke - marine and freshwater animals that live in almost all latitudes. The radially symmetrical body of cnidaria has one of two types of physique - polypoid or jellyfish. Representatives of the first type differ significantly in appearance, some are more like plants. In jellyfish, the oral cavity and tentacles are directed downward. As a rule, these coelenterates swim freely, and two forms of the body alternate in different generations. Almost all cnidaria have stinging cells; they are located on the tentacles. There are fewer freshwater intestinal than marine ones. Among them are single and colonial organisms.
The Shrews type combines the following animal classes:
- hydroid (Hydrozoa);
- scyphoid (Scyphozoa);
- coral polyps (Anthozoa);
- Cubomedusa (Cubozoa);
- polypodia (Polypodiozoa).
How are stinging cells arranged?
Translated from the Greek language, the word "cnidos" means "nettle", which is associated with the presence in the outer cover of animal capsules filled with poisonous secretions. As a rule, stinging cells are concentrated in the tentacles of cnidaria and are equipped with a sensitive cilia. Inside the knidocyte is a small pouch and a folded miniature tube - stinging thread. It looks like a compressed spring with a harpoon. An important role in the activation of burning cells belongs to calcium ions, a change in the concentration and pressure of the solution inside the capsule. It should be noted that cnidarians do not respond to all external stimuli, so as not to waste stinging cells. On the animal’s body there are nerve endings, or receptors, that help detect changes in the environment.
What is the function of stinging cells?
A slight contact with the prey or the enemy, the change in water pressure from a moving object can lead to the stimulation of a sensitive hair. Knidocytes are also able to respond to protein substances. Here's what happens when exposed to a stinging cell:
- The lid opens on the top facing the environment.
- The stinging thread straightens and, with sharp spikes at the base, pierces the victim's body.
- Knidocyte entwined or glued to the prey.
- The poison released causes paralysis or burns.
- Having fulfilled their function, cnidocytes die, and instead, new ones develop after 48 hours.
Due to the high concentration and coordinated activity of the cnidocytes on the tentacles, the intestinal animals infect the predator or potential prey. Neurotoxins inside stinging capsules paralyze a small victim and cause burns in large organisms.
Who are the chasing animals hunting for?
In the course of the experiments, it was found that the cnidocyte ejects a “harpoon” and poison within 3 milliseconds after contact with another animal. Lightning fast cellular reaction has almost no analogues in living nature. Its speed and strength, with which the stinging thread is released, is enough for some crustaceans to penetrate the hard shells! Large representatives of the intestinal cavity attack fish and hermit crabs. But for most cnidarians, small organisms like plankton and benthos serve as a food source. It should be noted that even stinging cells do not save many intestinal cavities from predators. Possessing such formidable weapons in tentacles, they nevertheless become an object of hunting for other animals.
How do the “flowers” of the animal world eat?
Coral polyps form colonies in the seas and oceans. Sea anemones or sea anemones live alone, attaching their soles to stones, shells, rocks and reefs. The tentacles and mouth of the polyps, which belong to the Anthozoa class, are usually located at the top, the lower part is attached to the substrate. The mouth of the sea anemone is surrounded by tentacles, on which are knidocytes. The function of the stinging cells of sea anemones is to attack prey and defend against enemies. Sea anemones are able to paralyze and entangle with burning threads of small animals. Some cnidarians draw out tentacles, which is necessary for an immovable lifestyle.
The problem of food production is also solved by the very fast action of stinging neurotoxins. Upon contact, they can immobilize prey and repel the attack of predators.
Where do hydroid animals live?
Representatives of the Hydrozoa class are found in fresh water bodies, Antarctic waters, and deep-sea ocean trenches. Hydra, limnomedusa, siphonophores, other subclasses and orders belong to this group. Most of them are predators that hunt with the help of cnidocytes. Gastrointestinal stinging cells, which are classified as hydroid, have significant differences in the size and strength of the poison. There is a separation of functions between groups of organisms in colonies of polyps: some feed, others protect, and others serve for reproduction. Some jellyfish get their food by drifting in water with motionless tentacles into which plankton falls, while others actively swim in search of food. There are intestinal cavities that are capable of purposefully hunting for a victim, the approach of which is signaled by receptors on the surface of the body.
Are scyphoid and cubomedusa knidocytes dangerous?
The sizes of animals belonging to the class Scyphozoa vary from 12 mm to 2.4 m across. Even large forms do not have a skeleton, head, or respiratory system. A typical representative of this group - translucent aurelia eared - is less toxic than other jellyfish. Adults feed on plankton adhering to tentacles. Scyphoid jellyfish have many cnidocytes and receptors surrounding the mouth and tentacles. Their main purpose is to recognize and paralyze prey.
Fatal for small animals are stinging cells of giant cyanoea (Cyanea arctica). And when in contact with a person, cnidocytes cause a burn of varying severity. Often there is a rash and redness from the effects of toxins that enter the skin. Cubomedusa - the inhabitants of the warm waters of the seas and oceans - are able to move quickly. Some of them are dangerous to humans: burns resulting from such "communication" can be fatal.
Intestinal and human
The problems of the relationship between humans and animals, which are of the type Stroke, are very diverse. Many divers and fans of beach holidays on the ocean are familiar with the stinging properties of intestinal. Stinging cells are characteristic of jellyfish floating in the water column. Even light contact with many of them can lead to painful conditions, burns, skin irritation. To enjoy diving or swimming, you just need to follow the rule, which reads as follows: "Watch, but do not touch." The best remedy for burns by tentacles of jellyfish is considered hot water, then a cold compress and taking antihistamines. One of the complex problems of interaction between the population and the intestinal cavity is the extraction of corals for the manufacture of jewelry, souvenirs. In recent years, the death of polyps - the builders of rich and complex underwater structures - has been alarming scientists. They create a habitat not only for themselves, but also for other invertebrates, as well as fish. Coral reefs in warm oceans and seas around the world are significantly affected by climate change, salinity and other water properties.
Colonies of polyps grow very slowly, increasing by only a few millimeters per year. Without coral buildings, it is difficult to imagine the underwater world, which so beckons with its unique beauty and special charm.