Among the aquatic invertebrates - the inhabitants of the seas, a group of organisms called scyphoids stands out. They have two biological forms - polypoid and medusoid, differing in their anatomy and lifestyle. In this article, the structure of the jellyfish will be studied, as well as the features of its life activity.
General characteristics of the Scyphoid class
These organisms belong to the type of coelenterates and are exclusively marine inhabitants. Scyphoid jellyfish, photos of which are presented below, have a bell-shaped or umbrella-shaped body, and it itself is transparent and gelatinous, consists of mesoglea. All animals of this class are secondary consumers and feed on zooplankton.
Organisms are characterized by radial (radial) symmetry of the body: anatomically identical parts, as well as tissues and organs, are located radially from the median longitudinal axis. It is inherent in animals that passively swim in the water column, as well as those species that lead a sedentary lifestyle (anemones) or slowly crawl along the substrate (marinestars, sea urchins).
External structure. Habitat
Since scyphoid representatives have two life forms - jellyfish and polyps, let's consider their anatomy, which has some differences. First, let's study the external structure of the jellyfish. Turning the animal with the base of the bell down, we will find a mouth fringed with tentacles. It performs two functions: it absorbs parts of the food and removes its undigested remnants to the outside. Such organisms are called protostomes. The body of the animal is two-layered, consists of ectoderm and endoderm. The latter forms the intestinal (gastric) cavity. Hence the name: type coelenterates.
The gap between the layers of the body is filled with a transparent jelly-like mass - mesoglea. Ectodermal cells perform supporting, motor and protective functions. The animal has a skin-muscular sac that ensures its movement in the water. The anatomical structure of the jellyfish is quite complex, since the ecto- and endoderm are differentiated into different types of cells. In addition to integumentary and muscular, in the outer layer there are also intermediate cells that perform a regenerative function (damaged parts of the animal's body can be restored from them).
The structure of neurocytes in scyphoid is interesting. They have a stellate shape and with their processes braid the ectoderm and endoderm, forming clusters - nodes. This type of nervous system is called diffuse.
Entoderm and its functions
The inner layer of the Scyphoid forms the gastrovascular system: the digestive canals, lined withglandular (secreting digestive juice) and phagocytic cells. These structures are the main cells that break down food particles. Digestion also involves the structures of the skin-muscular sac. Their membranes form pseudopodia, capturing and drawing in organic particles. Phagocytic cells and pseudopodia carry out two types of digestion: intracellular (as in protists) and cavitary, inherent in highly organized multicellular animals.
Stinging cells
Let's continue to study the structure of the scyphoid jellyfish and consider the mechanism by which animals defend themselves and also attack potential prey. The scyphoids also have one more systematic name: the class cnidaria. It turns out that in the ectodermal layer they have special cells - nettle, or stinging, also called cnidocytes. They are found around the mouth and on the tentacles of the animal. Under the action of mechanical stimuli, the thread located in the capsule of the nettle cell is rapidly ejected and pierces the body of the victim. Scyphoid toxins penetrating through the cnidocoel are fatal to planktonic invertebrates and fish larvae. In humans, they cause symptoms of urticaria 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 bodies - ropalia. They contain two sense organs: vision (eyes that react to light) and balance (statocysts that look like limestone stones). With their help, the scyphoid learn about the approaching storm:sound waves in the range from 8 to 13 Hz irritate the statocysts, and the animal hastily goes deep into the sea.
Reproductive system and reproduction
Continuing to study the structure of the jellyfish (the figure is shown below), let's focus on the reproductive system of scyphoids. It is represented by gonads formed from the pockets of the gastric cavity, having an ectodermal origin. Since these animals are dioecious, eggs and sperm are released through the mouth and fertilization occurs in the water. The zygote begins to split and a single-layer embryo is formed - the blastula, and from it - the larva, called the planula.
She swims freely, then attaches to the substrate and turns into a polyp (scyphistoma). It can bud and is also capable of strobilation. A stack of young jellyfish called ethers is formed. They are attached to the central trunk. The structure of a jellyfish that has broken away from the strobilus is as follows: it has a system of radial canals, a mouth, tentacles, ropalia and rudiments of the sex glands.
Thus, the structure of the jellyfish differs from the asexual individual of the scyphistoma, which has a cone shape of 1-3 mm and is attached to the surface with a stalk. The mouth is surrounded by a halo of tentacles, and the gastric cavity is divided into 4 pockets.
How Scyphoid move
Medusa is capable of jet propulsion. She abruptly pushes out a portion of water and moves forward. At the same time, the animal's umbrella is reduced to 100–140 times per minute. Studying the structure of the scyphoid jellyfish,for example, Cornerot or Aurelia, we noted such an anatomical formation as the skin-muscular sac. It is located in the ectoderm, efferent fibers of the marginal nerve ring and nodes approach its cells. The excitation is transmitted to the skin-muscular structures, as a result of which the umbrella contracts, then, straightening out, pushes the animal forward.
Features of ecology of scyphoids
These representatives of the coelenterates are common both in warm seas and in cold Arctic waters. Aurelia is a scyphoid jellyfish, whose body structure we studied, lives in the Black and Azov Seas. Another representative of this class, the cornerot (rhizostomy), is also widespread there. It has a milky white umbel with purple or blue edges, and the outgrowths of the oral lobes are similar to roots. Tourists vacationing in the Crimea know this species well and try to stay away from its representatives while swimming, since the stinging cells of the animal can cause serious "burns" of the body. Ropilema, like Aurelia, lives in the Sea of Japan. The color of her ropalia is pink or yellow, and they themselves have numerous finger-like outgrowths. The mesoglea of the umbrella of both species is used in the cuisine of China and Japan under the name "crystal meat".
Cyanea is the largest jellyfish in the cold Arctic waters. 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 hairy cyanide has two subspecies: Japanese and blue. venom of stinging cells,located along 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 features of their life.
