Shellfish

Shellfish, mollusks, the type of invertebrate animals, which includes snails, slugs, oysters, octopus, etc. There are more than 70,000 modern species and a large number of minerals. All shellfish, in principle, bilaterally symmetrical unsegmented body. Most have a sink in adulthood, and the rest - in the embryonic. The wall in the typical case it consists of three layers: a thin outer, konhiolinovogo (periostracum), which is a sink in the main owes its color, medium, prismatic (ostracum), consisting of calcium carbonate crystals, and internal (gipostrakuma) pearl. These layers are deposited skinfold - mantle. Although outwardly the representatives of different groups of mollusks vary greatly, they all share a number of characteristic structures, in particular foot, which the snail uses to crawl, perlovitsa - for burrowing into the bottom, and squid - for catching prey. Clams live in the seas, fresh water and on land. Depending on the symmetries and features of foot, mantle, nervous system and their shells are divided into five classes.Bokonervnye. The name of the class comes from the Greek. amphi - on both sides, and the neuron - a nerve. This marine forms, living mostly on the bottom of the shallow coastal waters. There are about 630 species. A typical representative - the coat. The body is bilaterally symmetrical bokonervnyh, sometimes vermiform, usually with inconspicuous head. Their shell is usually composed of eight transverse calcareous plates that cover the back. They feed on algae and shellfish, these hydroids.
 Gastropods. The name of the class comes from the Greek. gastr - belly, and pous - foot.These mollusks are different asymmetrical body, usually enclosed in a spiral shell, clearly visible head, and a broad flat foot. Well-known representatives of the gastropods, which include about 49,000 species - snails and slugs. In the past, as in some other form, shell rudimentary or absent, sometimes conical, not twisted into a spiral. Most gastropods - aquatic animals and terrestrial species are usually confined to moist habitats. Some live a parasitic lifestyle. Helix pomatia, type of Busycon canaliculatum, common on the Atlantic coast of the U.S., abalone and trumpeter widely used in food. Shells of many gastropods are the manufacture of various products, such as buttons. Some species - dangerous enemies of commercial shellfish. Small form ulitkopodobnye oyster drill and destroying Eupleura caudata oysters and mussels in their shells prosverlivaya round holes and eating away the soft parts. A large number of other bivalves and snails kill Polynices heros and Neverita duplicata. Marine Sandals (Crepidula fornicata) sometimes appear on the oyster beds in such large quantities that the oysters themselves under them almost invisible, and these valuable commercial shellfish die. At the head of a typical gastropod are one or two pairs of tentacles and a pair of eyes. The foot is the ventral part of the body, through which the animal crawls. The shell is secreted by the mantle and are usually twisted, and the growth of the animal to its new turns added. Many gastropods dioecious, others - hermaphrodites. Most of the species - egg-laying, and they lay eggs in protective capsules, but are known and viviparous forms of giving birth miniature copies of adult animals. Some marine gastropods from the eggs hatch into planktonic larvae.
 Lopatonogie or ladenogie. The name of the class comes from the Greek. skaphe - a boat, and pous - foot. This benthic marine animals found on the shallow water to a depth of 5 km. We know about 200 and 350 modern species extinct. Found in all seas except polar. The body is bilaterally symmetrical, elongate, covered with a slightly curved tubular shell. The head is reduced to a proboscis with mouth opening, heart, too rudimentary - no auricles. The animals are dioecious. To this class belongs the so-called Marine tooth.
 Bivalve, lamellibranch, or. The name of the class comes from the Greek. ax, and a leg.This is a balanced aquatic, mostly marine, bivalve mollusks from the shell, but without a head. Oysters, oyster, mussels, scallops - all these bivalves. The class consists of approx. 10,000 extant species, of which about 80% lives in the salty waters. There are basically shallow. Some, such as oysters, are sedentary, attaching to hard surfaces byssus threads or cement, while others may slowly crawl along the bottom, and even swimming (scallops). Many bivalves are able to burrow into the ground, and a small number of species may drill wood and even stone. Representatives of this class are fed mainly by microscopic plankton and detritus particles, strain off from the surrounding water. Many bivalves are of great commercial importance. Great production brings income oysters. Among many other edible species are the most popular hard shell and shell sand. In the food is used as mussels and scallops. Most species are dioecious this class, but quite common in it and androgyny. Sperm and eggs are usually released into the water, where fertilization takes place, but sometimes, for example, in freshwater mussels and perlovits, it occurs on the gills of the parent, and there begin the development of the larvae.Cephalopods. The name of the class comes from the Greek. head and leg. This is a highly organized clams, sometimes very large size, with a large head, well developed eyes and mouth around a crown of long tentacles, or arms. Structurally, they have the same as that of other mollusks, but the form and way of life is completely different. This class includes squids, cuttlefish, octopus and nautilus (ships). Cephalopods - predators that feed on vertebrates, molluscs and crustaceans. Many species are able to swim quickly, pushing the water from the mantle cavity through the siphon tube, and sometimes with fins. Octopuses normally crawl along the bottom, using his long tentacles. For cephalopods is the largest modern invertebrate - the giant squid Architeuthis princeps, whose length is 15 m
 In many countries, representatives of this class are used in food, and small squid fishermen often serve as bait. Of the shells of some species, such as nautilus, make jewelry. For cephalopods is about 400 modern species and ca. 5000 minerals.