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 both in salt and in fresh water it is very often possible to find a lot of inhabitants, and the most common of them are seashells 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 consider such peculiar growths for hours. In addition, such residents play a crucial role in the ecosystem.
Description, appearance
Like many species of mollusks, the river zebra mussel has a strong protective shell, consisting of two identical valves, forming an angle from the back. Ahead, the "house" of the underwater inhabitant is rounded. In length, it reaches 5 cm, and in width - 3. Dark zigzag or even stripes are clearly visible on the surface of the shell, while its main color can be yellowish, green or blue.
It is noteworthy that shells such as Dreissena polymorpha do not have lock teeth. Inside the flaps (on the front of them) a jumper is formed, on which the muscle-contactor is attached. The edges of the mantle are fused, but they still have holes for short siphon tubes and legs that help the mollusk to move. It is worth noting that the shell body itself is covered with cilia, capable of absorbing water into the mantle.
Lifestyle
Such inhabitants of fresh water bodies as zebra mussel do not conduct 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 in the dark. Movement is carried out using a weak narrow leg with a peculiar fossa located on the lower surface. Dreissena river breathes due to the gills, consisting of two parts. They are connected by threadlike petals and also serve as a filter for the process of separating water from different microparticles.
Basically, shells feed on plankton, but sometimes other elements fall into the mantle cavity, which become an excellent addition to the diet. Initially, food enters the stomach and intestines, where digestion occurs. Then the mass in processed form returns back to the mantle, from where it is washed out completely due to the water inside.
In addition, with proper nutrition of zebra mussel, the river grows very rapidly, increasing annually in size. This process does not stop throughout the life of the cochlea. Of course, among the representatives of the species there are also centenarians, but basically the life expectancy is about 4-5 years.
How is the breeding process
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 out eggs in the water (several at a time), located in mucus-filled pouches. Then external fertilization occurs, after which larvae called veligers appear. They swim for several days, growing tiny shells, and grow quite intensively, quickly gaining similarity with adults. Plunging to the bottom, the larva finds a suitable place for further life and releases bead threads (a special hardening mucus) that help attach to the surface. So, young animals can overlap each other in layers, which absolutely does not interfere with the usual way of life.
It is worth noting: these river bivalves are dioecious, unlike other small representatives of the species.
Habitat
Despite the fact that seashells are called river, they still prefer slightly salty water, which is why they are more common in fresh parts of the sea. They densely populate the Black, Azov, Aral and Caspian seas. The habitat extends from Europe to Western Kazakhstan. Veligers are also sometimes found in the rivers of Asia, in the Volga and Dnieper. These inhabitants of fresh water reservoirs are travelers, therefore they independently capture and settle in new places, due to which they spread throughout many reservoirs of the world. In addition, the snail feels comfortable at a depth of 1-2 meters, but sometimes drops to 10 and even 60 meters.
It is worth noting that seashells do not live in the northern regions, where it is very cold for them.
Aquarium Maintenance
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 shellfish. And this is correct, because they perform not only a decorative function in tanks, but also perfectly purify water, filtering it during the digestion process. However, when populating 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;
- an abundance of small river algae is needed;
- mollusks do not need additional food;
- water temperature should not be lower than 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 also does not emit harmful substances.
Role in the ecosystem
Long-term observations of zebra mussel allowed scientists to establish that it is an excellent filter of ponds, as it is able to absorb ordinary water and release purified water. 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 river shell cleans at least 10 liters of water daily. Small snails of zebra mussel (weighing 1 gram) need a large amount of food necessary for rapid growth, therefore they process at least 5 liters per day. So, large accumulations of mollusks quite quickly clean ponds.
In addition, these unpretentious lovers of fresh and brackish water do not mind eating fish, crayfish, and other types of snails. Therefore, people sometimes use zebra mussel as a mormyshka during fishing.
Often, the mollusk is also found in aquariums, since it prevents the appearance of turbidity in the tank, provides additional cleaning and improves the microenvironment.