The underwater world is full of magic and mysteries, because sometimes it is not so easy to find out what is hidden at the bottom of the reservoir. But in both s alt and fresh water, you can often find many inhabitants, and the most common of them are river shells, belonging to the class of bivalves. They are attached to the hulls of sunken ships or boats, snags, underwater piles and pipes. And a person is able to examine such peculiar growths for hours. In addition, these inhabitants play a vital role in the ecosystem.
Description, appearance
Like many types of mollusks, river zebra mussel has a strong protective shell, consisting of two identical flaps forming an angle from the back. Ahead, the “house” of the underwater inhabitant is distinguished by a rounded shape. In length, it reaches 5 cm, and in width - 3. On the surface of the shell, dark zigzag or even stripes are clearly visible, while its main color can be yellowish, green or blue.
Remarkably, shells such as Dreissena polymorpha do nothave locking teeth. Inside the valves (on their front part) a jumper is formed, on which the closing muscle is attached. The edges of the mantle are fused, but they still have holes for short siphon tubes and legs that help the mollusk move. It is worth noting that the body of the shell itself is covered with cilia that can absorb water inside the mantle.
Lifestyle
Such inhabitants of fresh water bodies as Dreissena do not lead an active life, preferring to adjoin underwater objects and not move all day. However, after sunset, the mollusks occasionally begin their “journey”, managing to overcome only 10 cm during the dark time of the day. Movement is carried out with the help of a weak narrow leg with a kind of hole located on the lower surface. The river mussel breathes due to the gills, which consist of two parts. They are connected by filamentous petals and also serve as a filter for the process of separating water from various microparticles.
Mostly, shells feed on plankton, but sometimes other elements get into the mantle cavity, which become an excellent addition to the diet. First, food enters the stomach and intestines, where digestion takes place. Then the processed mass returns back to the mantle, from where it is completely washed out due to the water inside.
In addition, with proper nutrition, the river mussel grows very quickly, increasing in size every year. This process does not stop throughout the entire period of the existence of the snail. Of course, among the representatives of the species there are alsocentenarians, but generally life expectancy is about 4-5 years.
How does the process of reproduction
With the onset of spring, when the water temperature gradually warms up, river zebra mussel absorbs male germ cells into the mantle cavity, where fertilization begins. After a while, she spits eggs into the water (several pieces at a time), located in sacs filled with mucus. Then external fertilization occurs, after which larvae called veligers are born. They swim for several days, growing tiny shells, and grow quite intensively, quickly becoming similar to adults. Plunging to the bottom, the larva finds a suitable place for further life and releases bead threads (a special hardening mucus) that help to attach to the surface. So, young animals can overlap each other in layers, which absolutely does not interfere with their usual way of life.
Note: These river bivalves are dioecious, unlike other small members of the species.
Habitat
Despite the fact that shells are called river shells, they still prefer slightly s alty water, which is why they are more common in fresh parts of the sea. Very densely they inhabit the Black, Azov, Aral and Caspian Seas. The habitat ranges from Europe to Western Kazakhstan. Also, veligers are sometimes found in the rivers of Asia, in the Volga and Dnieper. These inhabitants of fresh water are travelers, therefore, on their ownthey capture and settle in all new places, due to which they spread to many water bodies of the world. In addition, the snail feels comfortable at a depth of 1-2 meters, but sometimes sinks to 10 or even 60 meters.
It should be noted that river shells do not live in the northern regions, where it is very cold for them.
Content in aquariums
Probably, almost every aquarist seeks to diversify his small “home pond” in every possible way, therefore, along with fish and algae, he often acquires snails with mollusks. And rightly so, because they perform not only a decorative function in the tanks, but also perfectly purify the water, filtering it during the digestion process. However, when populating a zebra mussel in a container, it is important to remember that in order for it to cope with the task, it is necessary to adhere to certain rules:
- since the snail grows rather big, it is recommended to keep it in a container with a volume of at least 90 liters;
- requires abundance of small river algae;
- shellfish do not need additional feed;
- water temperature should be at least 18-25 degrees.
It is worth noting that this representative of the species is quite peaceful, therefore it does not harm its neighbors, does not eat caviar and algae, and does not emit harmful substances.
Role in the ecosystem
Long-term observations of zebra mussel have allowed scientists to establish that it is an excellent filter-feeder of water bodies, since it is able to absorb ordinary water and releasepurified. The liquid passed through the mantle is saturated with special substances that help algae grow at an accelerated pace. Experts have proven that an adult individual of the river shell purifies at least 10 liters of water daily. Small zebra snails (weighing 1 gram) need a large amount of food necessary for rapid growth, so they process at least 5 liters per day. So, large accumulations of mollusks clean up water bodies rather quickly.
In addition, these unpretentious lovers of fresh and brackish water are not averse to eating fish, crayfish, and other types of snails. Therefore, a person sometimes uses zebrafish as a mormyshka while fishing.
The mollusk is also often found in aquariums, as it prevents the appearance of turbidity in the tank, provides additional cleaning and improves the microenvironment.
