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Marine and freshwater (river) species of bivalve mollusks

Bivalve mollusks (Bivalvia) are distinguished by a shell consisting of two parts (valves). This class has a few more names describing the representatives of this class. For example, Lamellibranchia are plate-like mollusks, whose gills really consist of plates.

Acephala are headless mollusks that have lost their head in the process of evolution. Pelecypoda (tooropivye) – the name describes the form of bivalve limbs.

There are several species of bivalve mollusks, having a name describing their external features.

The second largest group of mollusks after gastropods consists of more than 20 thousand species. All these species are benthic, that is, benthic. Bivalves live at the bottom of ponds with fresh or salt water.

Most Bivalvia are extremely slow. or lead an almost motionless lifestyle.

For example, the speed of movement across the bottom of the representatives of the species of river bivalve mollusks – toothless – no more than 20-30 cm per hour. And oysters, for example, attach to the substrate in the larval stage and are incapable of movement at all.

The evolutionary changes associated with the disappearance of the head and the radula (from the Latin radula – scraper, squeegee, grater for scraping food) and the formation of the developed lamellar gills led to the establishment of such a little or no fixed lifestyle.

Bivalves live inactive at the bottom of reservoirs.

The depths inhabited by various species of the Bivalvia class vary from the tidal coastal zone to the sea depressions 10 km deep.

Bivalves eat organics and small plankton. Filtering the water suspension using a gill, they implement two functions at once: breathing, absorbing oxygen from water, and nourishment, draining foodable particles.

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Some groups of plate-waving have interesting adaptations to life on stones. Species belonging to the genus of pholas (Pholas) have sharp teeth for drilling in stone at the front end of the shell.

Another type of marine bivalve mollusks, called the sea dates (Lithophaga), although it does not have a drilling apparatus, is also able to penetrate into the stones, dissolving them with acid, which is secreted by special glands.

Inside the bivalve shell placed the body of the mollusk, consisting of the torso and legs. The leg is a muscular part of the body, by means of which the mollusks move along the bottom or burrow into the ground.

It is often wedge-shaped and capable of protruding from the shell.

Inside the shell is the body of the mollusk

In many species, for example, the mussel (Mytilus) has a byssus gland in the leg, emitting a substance that helps the mollusc to attach to stones and a similar substrate. Byssus is a strong thread.

Some adult mollusks do not have such a gland, in which case it most likely was developed at the larval stage.

The shells of the plate-crepe may be of various sizes and shapes. The smallest deep-sea mollusks do not grow more than 0.5 mm in length.

But there are giants, for example, tridacna – the inhabitant of coral reefs in tropical seas. The size of this bivalve species can reach 1.4 m in length with body weight up to 200 kg.

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Most species have a flattened oblong body. But there are also species of elongated worm-shaped or almost spherical shape. The shell can be symmetrical or have different size flaps.

Most of the representatives of bivalves have a lock on the shell flaps, which prevents the flaps from moving relative to each other.

Regardless of the shape and size of the sink consists of three layers:

  • external – konkholinovogo;
  • internal – calcareous;
  • bottom – mother of pearl.

The shell of a bivalve mollusk is thicker than that of a freshwater inhabitant

The thickness and strength of the shell in different species is also different and depends on the living conditions. A large amount of minerals in the water allows you to build a more durable calcareous skeleton, so the marine bivalves usually have a thicker shell than freshwater species.

The part of the body of the mollusk adjacent to the valves releases substances from which the shell consists. Thus, during the life of the sink gradually increases.

Among Bivalvia with a well-developed mother of pearl layer there are freshwater species (perlovitsa, freshwater pearl oyster, etc.) and marine (sea pearl oysters, etc.).

People living in close proximity to the shores of seas and rivers have long used Bivalvia as food. And from their shells and pearls they made household utensils and decorations.

For consumption as food, many plate-wound are used. The most common types are:

  • mussels (Mytilus);
  • heartworm (Cardium);
  • Oysters (Ostrea);
  • scallops (Pecten).

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Many bivalves under the sink as a result of irritation from a foreign body or parasitic invasion form pearls. The composition of pearls is the same as that of the shell, it consists of the same layers, only the pearlescent layer is on the outside.

The pearl oysters Pteria and Pinctada and the freshwater pearl oyster Margaritana margaritifera are considered commercial species for pearl harvesting.

At hit of a foreign irritant in a sink – the pearl is formed

At present, the mariculture of Bivalvia mollusks is widely developed, that is, their artificial breeding. They are grown for use in food or for pearls.

Founded in 1907 in Japan, the company was the first manufacturer of artificial pearls. Bivalvia was mined for this in the open sea, and it was only in the mid-50s that they managed to start growing pearl mussels themselves.

Foreign objects placed into the shell of the pearl oyster are gradually enveloped with nacre. And in 1-2 years it is possible to extract finished pearls, which are carefully sorted by size and shades and sent to enterprises for the manufacture of jewelry.

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The biofiltration ability of Bivalvia mollusks is considered a useful property of these living organisms. The direction considering the use of these animals for water purification is considered relevant. Mollusks are able to absorb and accumulate heavy metals in their body tissues and purify water from chemical and organic pollutants.

The average activity of the plate-like when filtering water is about 1 l per hour.

One of the most useful properties of these organisms is the ability to purify water.

The issue of protection and breeding Bivalvia for use as biofilters in fresh and marine waters is considered by scientists as one of the most pressing issues. In areas where commercial plate-breeding of plate-scale has been established, high-quality biological water purification, accumulation of bottom sludge, richer bottom fauna develops and the overall productivity of the ocean develops.

The dying mollusks form calcareous sedimentary rocks that form layers on the sea and ocean floor, which are the material for the formation of shell rock, marble, limestone. The fossil remains of the shells are the forms on which the determination of the age of the layers of the earth is based.

First of all, Bivalvia mollusks harm hydraulic structures and sea ships. Conducted an active development of special coatings that can protect vessels and structures from fouling pests.

Some species of mollusks are pests.

In the rivers and sea waters of the Black and Caspian Seas, where the bivalve mollusk of the species Dreissena Polymorpha dwells, large colonies of these animals can form, which are attached to hydraulic structures. These animals settle in water pipes and turbines of hydroelectric power plants, leading to blockages.

A well-known pest is the Bivalvia mollusc of the species Teredo navalis (or marten), also called the shipworm. It is found in the Black and Far Eastern seas, reaches a length of 18 cm and has a worm-like shape.

The sink occupies only one end and is adapted for drilling wood. The mollusk damages the wooden structures and the bottoms of ships.

To fight with tree borers, wood is smoked.

Some of the Bivalvia mollusks are parasitic carriers. Serving as an intermediate host for all sorts of parasitic worms, they can be a source of infection for predatory fish or birds.

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