The branch of biology that deals with the study of animal organisms that inhabit the globe is called zoology. One of its sections directly considers a group of multicellular animals - crustaceans. Their structure, life features, as well as the importance of crustaceans in nature and human life will be discussed in this article.
Crustacean taxonomy
Among the invertebrate organisms inhabiting our planet, animals stand out, which are combined into the Type Arthropods. Crustaceans are one of the superclasses of this taxon, whose representatives live mainly in fresh or sea water. Only a few of them, such as wood lice and land crabs, live in moist terrestrial areas. The Superclass Crustacea includes: the class of lower crayfish and the class of higher (decapod) crayfish.
In turn, each of these taxa consists of smaller systematic groups - orders. Lower crustaceans serve as the basis of zooplankton, so they have an importantimportance in nature and human life. In essence, being one of the first links in the food chains, lower crayfish are a food base for fish and aquatic mammals. Thanks to the representatives of the orders of isopods, copepods and cladocerans, marine life receives a complete protein food, since the body of lower crayfish includes easily digestible polypeptides.
The class of higher crustaceans includes one order - decapod crayfish, which is represented by such animals as crabs, lobsters, lobsters and shrimps.
Features of the structure of crustaceans
The division of animals into classes is based primarily on differences in the external structure of these organisms. In lower crayfish, such as cyclops (a detachment of copepods), daphnia (a detachment of cladocerans), wood lice (a detachment of isopods), the body contains a variable number of segments (segments), and there are no limbs on the abdomen. On its last segment there is a specific formation - a fork. The body itself has a soft and thin chitinous shell through which the internal organs of animals are visible.
The higher crustaceans, whose representatives have a hard chitinous shell impregnated with lime, are also distinguished by a strict division of the body into a cephalothorax and abdomen with a constant number of segments in them. So, crayfish have 5 and 8 segments in the cephalothoracic region, respectively, and the abdomen has 6 segments. Also, the higher crayfish, unlike the lower ones, have swimming legs on the abdomen.
Metabolism and vital activity
As mentioned earlier,The life of crustaceans takes place mainly in water. Therefore, they clearly manifest the so-called idioadaptations - adaptations to a specific habitat: breathing with the entire surface of the body or gills, a streamlined body shape, a shell consisting of chitin and impregnated with a water-repellent substance - calcium carbonate.
Crustacean systems, such as circulatory, respiratory and excretory, provide homeostasis - maintaining a normal level of metabolism. It should be noted that all crustaceans have an open circulatory system, and the heart looks like a pentagonal sac-shaped organ with 3 pairs of valves. From it to the cephalothorax and abdomen, arteries depart, through which blood carries nutrients and oxygen to all organs of the animal, pouring into a mixed body cavity called the mixocoel. From it, already venous blood enters the gills, where it is released from carbon dioxide and saturated with oxygen, turning into arterial blood. Through holes in the pericardial sac, it enters directly into the heart.
Shitni - a peculiar group of crustaceans
These animals, which are a group of freshwater inhabitants, can live in dry waters. When the water evaporates, the shield itself is buried in the soil and does not lose its viability for a certain time. Eggs laid by the female on the bottom of the reservoir can last up to 15 years. They are easily carried by the wind along with soil particles, so shieldworms live almost everywhere except for Antarctica and African deserts.
Crustacean life cycle
Representatives of this superclass have both its simple forms, for example, the direct development of crayfish, and more complex ones, including larval stages. In this case, the development is called indirect. It is characteristic of the orders of copepods and cladocerans, and is also found in higher crayfish, for example, lobsters or spiny lobsters. Crustaceans, whose representatives have pelagic or planktonic forms of larvae, the so-called nauplii and zoea, are widespread in nature: they are inhabitants of the coastal waters of Australia, North America, and Europe. All phases of the life cycle of crustaceans are controlled by their endocrine system, represented by androgenic, postcommissural and sinus glands. They secrete hormones that regulate the processes of puberty, molting, and the transformation of larvae into adults.
The importance of crustaceans in nature and human life
Animals belonging to the order of decapods, such as lobsters (lobsters), lobsters, crabs, are valuable commercial species that provide humans with delicious and high-protein meat. Representatives of lower crayfish are of great importance: cyclops, daphnia, water donkeys, which are food for fish, for example, such valuable ones as salmon and sturgeon.
River crayfish, often called orderlies, clean the bottom of dead organic matter. Although the significance of crustaceans in nature and human life is overwhelmingly positive, but some animals are harmful, for example,carp lice cause mass death of commercial fish species. And cyclops are intermediate hosts of parasitic worms: guinea worms and wide tapeworm.
We are convinced that these animals, which are part of the Arthropoda phylum, are an important link in the natural ecosystems of our planet and the importance of crustaceans in nature and human life should not be underestimated. Some species of these animals (for example, broad-toed crayfish, mantis shrimp) are listed in the Red Book, and their destruction is punishable by law.
