Among aquatic invertebrates - the inhabitants of the seas, a group of organisms called scyphoid is distinguished. They have two biological forms - polypoid and medusoid, differing in their anatomy and lifestyle. In this article, the structure of jellyfish will be studied, as well as the features of its vital functions.
General characteristic of the class of scyphoid
These organisms belong to the type of intestinal and are exclusively marine inhabitants. The scyphoid jellyfish, the photos of which are presented below, have a bell-shaped or umbrella-shaped body shape, and it itself is transparent and gelatinous, consists of mesogley. All animals of this class are second-order consumers and feed on zooplankton.
Organisms are characterized by radial (radiation) 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 (sea anemones) or slowly crawl along the substrate (starfish, sea urchins).
The external structure. Habitat
Since representatives of the scyphoid have two life forms - jellyfish and polyps, consider their anatomy, which has some differences. First, we will study the external structure of the jellyfish. Turning the animal with the base of the bell down, we find a mouth bordered by tentacles. It performs two functions: it absorbs parts of food and removes undigested residues to the outside. Such organisms are called primary organisms. The body of the animal is two-layer, consists of an ectoderm and an endoderm. The latter forms the intestinal (gastric) cavity. Hence the name: type of intestinal.
The gap between the layers of the body is filled with a transparent, jelly-like mass - mesoglay. Ectodermal cells perform supporting, motor and protective functions. The animal has a skin-muscle bag, providing its movement in water. The anatomical structure of 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 (from them damaged parts of the animal’s body can be restored).
The structure of neurocytes in scyphoid is interesting. They are star-shaped and with their processes surround the ectoderm and endoderm, forming clusters - nodes. The nervous system of this type is called diffuse.
Endoderm and its functions
The inner layer of the scyphoid forms a gastrovascular system: from the intestinal cavity, the digestive channels lined with glandular (secreting digestive juice) and phagocytic cells depart from the intestinal cavity. These structures are the main cells that break down food particles. The structure of the musculoskeletal sac is also involved in digestion. Their membranes form pseudopodia, capturing and drawing in organic particles. Phagocytic cells and pseudopodia carry out two types of digestion: intracellular (like a protist) and cavitary, inherent in highly organized multicellular animals.
Stinging cells
We continue to study the structure of the scyphoid jellyfish and consider the mechanism by which animals defend themselves and attack a potential victim. The Scyphoid have one more systematic name: the class of stalker. It turns out that in the ectoderm layer they have special cells - nettle, or stinging, also called knidocytes. They are located 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 thrown out and pierces the victim's body. Scyphoid toxins that penetrate the bookloid are fatal to planktonic invertebrates and fish larvae. In humans, they cause urticaria symptoms and skin hyperthermia.
Sensory organs
Along the edges of the jellyfish bell, the photo of which is presented below, you can see shortened tentacles, called marginal bodies - ropalia. They contain two sensory organs: vision (eyes that respond to light) and equilibrium (statocysts, which look like calcareous 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 leaves deep into the sea.
Reproductive system and reproduction
Continuing to study the structure of jellyfish (the figure is presented below), we will dwell on the reproductive system of the scyphoid. It is represented by gonads formed from the pockets of the gastric cavity, having ectodermal origin. Since these animals are dioecious, eggs and sperm go out through the mouth and fertilization occurs in water. The zygote begins to crush and a single-layer embryo, the blastula, is formed, and from it a larva called the planula.
She swims freely, then attaches to the substrate and turns into a polyp (scyphoid). It can be budged, and is also capable of gating. A stack of young jellyfish is formed, called esters. They are attached to the central trunk. The structure of the jellyfish, detached from the strobilus, is as follows: it has a system of radial channels, a mouth, tentacles, ropalia, and the rudiments of the gonads.
Thus, the structure of the jellyfish differs from the asexual specimen of the scyphistoma, which has a conical shape of 1-3 mm in size and is attached to the surface with the help of a stalk. The mouth is surrounded by a corolla of tentacles, and the gastric cavity is divided into 4 pockets.
How Scyphoid Moves
Jellyfish is capable of jet propulsion. She abruptly pushes a portion of water and moves forward. The umbrella of the animal is reduced to 100-140 times per minute. Studying the structure of the scyphoid jellyfish, for example, cornerotus or aurelia, we noted such an anatomical formation as a skin-muscle sack. It is located in the ectoderm, efferent fibers of the regional nerve ring and nodes are suitable for its cells. Excitation is transmitted to the skin-muscle structures, as a result of which the umbrella is compressed, then straightened, pushes the animal forward.
Features of the ecology of scyphoid
These representatives of the gastrointestinal class 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 is widely spread there - cornerot (rhizostoma). It has a milky white umbrella with purple or blue edges, and the outgrowths of the oral lobes are similar to the roots. Tourists vacationing in the Crimea are well aware of this species and try to be away from its representatives during bathing, as stinging animal cells 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-shaped outgrowths. Umbrella mesogley of both types is used in the cuisine of China and Japan under the name "crystal meat."
Cyanoea - an 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 hairy cyanide has two subspecies: Japanese and blue. The venom of stinging cells located on 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.