Difference between shellfish and worms

Not many will be inspired by the curves of the body of a worm or mollusk that has been pulled out of a shell. But, despite the unsightly appearance, one type of these animals is the source of the existence of entire industries in the national economy, another type can cause the depletion and death of a number of animal and human species.

Definition

Molluscs - these are spineless animals, the body of which is protected by a shell, united by one type.

Worms are spineless animals grouped into the Flatworm type.

Comparison

Flatworms are notorious for being parasites. Some of them, and these are 14 thousand species, can live in the body of an animal, in the internal organs of a person, and some exist in the natural environment, inhabiting seas, oceans, fresh water bodies and tropical rainforests. The length of flatworms varies from 1 mm to 30 meters. This length is reached by the parasites that live in the intestines of the sperm whale.

Flatworms have a body in the form of a leaf or a ribbon. In the process of evolution, they acquired bilateral symmetry of the body. The integument of the body of the worm is represented by the musculocutaneous sac. The nervous system is differentiated into central and peripheral. In flatworms, organ systems such as excretory, reproductive and digestive systems are formed. The latter system is built on a closed type, and in parasites it is completely absent. The channels of the excretory system permeate the entire body of animals. The external integuments are involved in breathing. Flatworms lack a body cavity, and the space between the internal organs is filled with loose connective tissue. Most flatworms are hermaphrodites. They have internal fertilization, but they can reproduce and vegetatively.

Flatworms live in fresh and salt water bodies, in moist soil, in the organs and tissues of other living creatures. Parasitic forms of worms during their life cycle can change several hosts. For example, a feline fluke goes from an egg to the stage of a larva, which enters the body of a mollusk (intermediate host), from it to a fish (intermediate host), and with it to a cat, the main “host”.

Molluscs are spineless animals with a soft, asymmetrical body, which is often hidden in a shell. These organisms live in fresh (pond snail) and salty (mussels, oysters, octopus and squid) bodies of water. Most mollusks do not exceed several tens of centimeters in size, but there are also real giants. For example, a tridacna, the length of the shell valves of which is 150 cm, and the mass is 280 kg.

Different types of molluscs eat different foods - plants, hunt other living organisms, eat carrion. Of the 130 thousand species of mollusks, a significant part is occupied by passive filter feeders, several dozen species of mollusks are parasitized.

Perlovitsa. A representative of mollusks

In the body of a mollusk, three sections are distinguished - the head, trunk and leg. The body of the animal is covered with a shell, single or bivalve. It is synthesized by the mantle. The mollusc has no musculocutaneous sac. Muscles are represented by separate bundles. The body cavity is filled with loose connective tissue. The circulatory system of animals is of an open type, but they already have a heart. There are specialized respiratory organs - gills and lungs. The digestive system consists of three sections: the digestive, salivary glands, and the liver. The excretory organs are the kidneys. The central nervous system is built on a scattered-nodal type. Molluscs can be dioecious and hermaphrodites, fertilization in them takes place internally or externally, ontogenesis can be direct or indirect.

Molluscs are food for humans and animals. In some species, pearls are synthesized in the shells, and the valves of the hard integument are the material for the manufacture of mother-of-pearl. Previously, shellfish were used as fertilizer.

Conclusions TheDifference.ru

  1. The body of the mollusk is divided into sections, the body of the worm is devoid of such differentiation.
  2. The body of worms is symmetrical, of mollusks - asymmetric.
  3. In addition to the hydrosphere and excessively humid areas of the earth's surface, in which representatives of both types can be found, many species of worms inhabit the internal organs and tissues of other living organisms.
  4. Molluscs have a more complex organization of all organ systems than worms.
  5. The significance of the existence of flatworms for humans is rather negative, but mollusks are a source of increased demand among gourmets and cooks, farmers, jewelers, manufacturers of luxury goods and souvenirs.
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