The structure of the jellyfish. The structure of the scyphoid jellyfish

Among aquatic invertebrate animals - the inhabitants of the seas, a group of organisms called scythoid organisms is distinguished. They have two biological forms - polypoid and medusoid, differing in their anatomy and way of life. In this article, the structure of the jellyfish will be studied, as well as the features of its life activity.

General characteristics of the class Scyphoid

These organisms are of the coelenterated type and are exclusively marine. Scythian jellyfish, the photos of which are presented below, have a bell-shaped or umbrella-shaped body, while it itself is clear and gelatinous, consists of mesogloea. All animals of this class are consumers of second order and feed on zooplankton.

For organisms, the radial (ray) symmetry of the body is characteristic: anatomically identical parts, as well as tissues and organs are located radially from the median longitudinal axis. It is inherent in animals passively floating in the water column, as well as those species that lead a sedentary life (anemones) or slowly creep along the substrate (sea stars, sea urchins).

External structure. Habitat

Since representatives of Scythoid have two life forms - jellyfish and polyps, we will consider their anatomy, which has some differences. First we study the external structure of the jellyfish. Turning the animal upside down, we find a mouth bordered by tentacles. It performs twofold functions: it absorbs portions of food and removes undigested remains of it outside. Such organisms are called primary. The animal's body is two-layered, consists of ectoderm and endoderm. The latter forms the intestinal (gastral) cavity. Hence the name: type coelenterates.

The space between the layers of the body is filled with a transparent jelly-like mass - mesogloe. Ectodermal cells perform supporting, motor and protective functions. The animal has a dermo-muscular sac that provides its movement in the water. The anatomical structure of the jellyfish is quite complex, because the ecto- and endoderm are differentiated into different types of cells. In addition to integumentary and muscular, in the outer layer there are still intermediate cells performing a regenerative function (from which damaged parts of the animal's body can be restored).

The structure of neurocytes in Scyphoid is of interest. They have a stellate shape and their braids braid the ectoderm and endoderm, forming clusters - nodes. A nervous system of this type is called diffuse.

The endoderm and its functions

The inner layer in the Scyphoid forms a gastrovascular system: from the intestinal cavity the rays leave the digestive channels lined with glandular (excreting digestive juice) and phagocytic cells. These structures are the main cells that break down food particles. In the digestion also involved structures of the skin-muscle sac. Their membranes form pseudopodia, which capture and draw in organic particles. Phagocytic cells and pseudopodia carry out two types of digestion: intracellular (like protista) and cavitary, inherent in highly organized multicellular animals.

Streptococcal cells

We continue to study the structure of the scyphoid jellyfish and consider the mechanism by which animals protect themselves, and also attack a potential victim. Scythoid ones also have one more systematic name: the class is shining. It turns out that in the ectodermal layer they have special cells - nettle, or stinging, also called cnidocytes. They are around the mouth and on the tentacles of the animal. Under the action of mechanical stimuli, the filament found in the capsule of the nettle cell is rapidly thrown out and pierces the victim's body. Scythoid toxins penetrating through the cnidocoel are deadly to plankton invertebrates and fish larvae. In humans, they cause symptoms of hives and hyperthermia of the skin.

Sense organs

On the edges of the bell of the jellyfish, the photo of which is presented below, you can see shortened tentacles, called marginal corpuscles - ropalias. There are two sensory organs in them: the eyes (the eyes that react to light) and the equilibria (statocysts having the appearance of calcareous stones). With their help Scythians learn about the approaching storm: sound waves in the interval from 8 to 13 Hz irritate the statocysts, and the animal hastily goes deep into the sea.

Sexual system and reproduction

Continuing to study the structure of the jellyfish (see the figure below), we will focus on the reproductive system of Scyphoid. It is represented by gonads formed from the pockets of the gastric cavity, having an ectodermal origin. Since these animals are dioecious, ovules and spermatozoa go through the mouth and fertilization occurs in the water. Zygote starts to crush and forms a single-layer bud - the blastula, and from it - a larva, called a planula.

It freely floats, then attaches to the substrate and turns into a polyp (scifistome). It can be repaired, and also capable of stroking. A pile of young jellyfish, called ethers, is formed. They are attached to the central trunk. The structure of the jellyfish that detached itself from the strobila is as follows: it has a system of radial canals, mouth, tentacles, ropalia, and the rudiments of the sex glands.

Thus, the structure of the jellyfish differs from the asexual specimen of the scifistome, which has a conical shape of 1-3 mm and is attached to the surface by means of a stalk. The mouth is surrounded by a whisk of tentacles, and the gastric cavity is divided into 4 pockets.

How does the Scythoid

Medusa is capable of reactive movement. She sharply pushes out a serving of water and moves forward. The umbrella of the animal is reduced to 100-140 times a minute. Studying the structure of the scyphoid jellyfish, for example, corneroth or aurelia, we noted an anatomical formation, such as a skin-muscular sac. It is located in the ectoderm, efferent fibers of the marginal nerve ring and nodes approach its cells. Excitation is transmitted to the musculoskeletal structures, resulting in the umbrella contracting, then straightening, pushing the animal forward.

Features of ecology Scythoid

These representatives of the coelenterate class are common both in warm seas and in cold arctic waters. Aurelia - a scyphoid jellyfish, whose body structure we studied, lives in the Black Sea of Azov. Another representative of this class, the coronerot (rhizostoma), is also widely distributed there. He has a milky white umbrella with purple or blue edges, and the outgrowths of the mouth blades are similar to the roots. Holidaymakers in the Crimea tourists know this species well and try to be away from their representatives during bathing, since the stinging cells of the animal can cause serious "burns" of the body. Ропилема, as well as арелия, dwells in the Sea of Japan. Its color is pink or yellow, and they themselves have numerous finger-shaped outgrowths. The mesogloe umbrella of both species is used in the kitchen of China and Japan under the name "crystal meat".

Cyanea - the inhabitant of cold arctic waters, is the largest jellyfish. The length of its tentacles reaches 30-35 m, and the diameter of the umbrella is 2-3.5 m. The lion's mane or cyanide hairy has two subspecies: Japanese and blue. The poison of the stinging cells located at the edges of the umbrella and on the tentacles is very dangerous for humans.

We studied the structure of scyphoid jellyfish, and also got acquainted with the peculiarities of their life activity.