Our article is devoted to amazing representatives of the animal world - mollusks. Thanks to the peculiarities of their structure, they have mastered both the water and land-air habitats. These organisms have a number of structures inherent only to them. What is the digestive gland in mollusks, as well as the mantle cavity, grater, lock, funnel? Let's figure it out together.
Features of the structure of mollusks
The name of this systematic unit in Latin means "soft". And indeed mollusks (the photo below shows one of the representatives of the type) are invertebrates. Their soft, non-segmented body is often protected by a shell and consists of three parts: the head, trunk and legs. Each of them carries a number of organs.
On the head is a pair of tentacles, which serve as an organ of touch. The leg is on the ventral side of the body, providing movement of the mollusks. The trunk of animals is surrounded on all sides by a fold of covers, which is called the mantle. As a result, a cavity is formed between this structure and the body. It contains respiratory organs, opens the channels of the digestive, excretory and reproductive systems.
Note that the mollusks, the photos of which are presented in our article, differ substantially in their external features. Depending on these characteristics, three classes are distinguished: the Bruxo- and the cephalopods, the Bivalves. Representatives of the first group have mastered not only water bodies, but also various areas of land: soil or forest litter. The gastropods are well developed all parts of the body. The trunk of most of them is located inside a spirally twisted shell.
The body of cephalopods consists of legs and trunk, and the leg is modified into tentacles. A characteristic feature of this class is the ability to reactive motion. This is possible due to the presence of a special tubular formation - a funnel. It is a modified part of the leg.
Bivalve mollusks live exclusively in water bodies. They do not have a head; therefore, parts of the organs are also missing: tentacles, pharynx, tongue with grater, salivary glands. Their shell consists of two valves, which in most species have protrusions and indentations. Their totality is called a castle.
Structure of the digestive system
All mollusks have a digestive system of a through type. In the Brukho- and Cephalopods, it begins with a mouth opening. Horny jaws are located on its border with the pharynx. With their help, shellfish scrape off food from various surfaces. The anal opening, which ends the given system, opens into the mantle cavity.
The main digestive gland of mollusks is the liver. It is the outgrowth of the midgut. Most species have salivary glands. Almost all the cephalopod mollusks excrete poisonous substances, through which they paralyze and kill prey.
What is the digestive gland in shellfish?
This part of the digestive system is also called hepatic-pancreatic or hepatopancreatic iron. Through specialized excretory ducts, it retains a connection with the intestine. Digestive gland in mollusks is involved in the digestion and absorption of organic substances. It is a place of storage of fats and carbohydrates, and also carries out phagocytosis.
What is the digestive gland in mollusks, which belong to the class of cephalopods? Representatives of this group are characterized by more specialized structures. They separately have a liver, pancreas and salivary glands.
Types of food: Bivalves and cephalopods
Features of the structure of the digestive system of each class of mollusks and the type of their food vary. For example, Bivalves are typical filter feeders. To do this, they use special structures called siphons. They are of two types. Water enters the inlet siphon with suspended organic particles. In the mantle cavity it is filtered. With the help of cilia, food enters the mouth opening. After passing through the tract, it enters the discharge siphon.
The majority of cephalopods are predators. On their tentacles are located suckers, which help catch and hold prey. They feed on crustaceans, fish and other mollusks. In the oral cavity of the cephalopods there are grater and horny jaws. They are so powerful that they can crush even the shells of crabs. To attract production, these mollusks have special organs of luminescence. And to protect themselves from enemies, they use ink glands. When a secret enters the water, a dark spot forms under the cover of which the animal is hiding.
Features of shellfish feeding: Gastropoda class
These mollusks, in the prevailing number of cases, are herbivorous. When traveling, they scrape off the algae with the help of a grater and horny jaws. What is the digestive gland in shellfish of this class, which are predators? Some of these species include sulfuric acid in the saliva. It is capable of dissolving the shells of victims or the poison of enemies. Such predatory gastropods use a grater only to retain prey.
Once in the mouth, the food particles stick to the viscous saliva. Numerous cilia, which are in the throat, send this lump into the stomach. At its pointed end is a special structure called prostil. It is formed by sedimentary particles. Prostyle acts like a reel, separating food particles from saliva.
Surprisingly, the mollusc saltmus is fed. Their digestive system is completely reduced. Scientists suggest that they use chemosynthetic bacteria to assimilate food .
So, mollusks are invertebrates, which have a soft, non-segmented body. They have a digestive system of the through type, as well as specialized glands: salivary, pancreatic and liver. The method of feeding mollusks can be grouped into three large groups: filter feeders, herbivores and predators.