Our article is dedicated to the amazing representatives of the animal world - mollusks. Due to the peculiarities of their structure, they have mastered both aquatic and airborne habitats. These organisms have a number of structures unique to them. What is the digestive gland of mollusks, as well as the mantle cavity, grater, castle, funnel? Let's figure it out together.
Features of the structure of mollusks
The name of this systematic unit in translation from Latin means "soft". And indeed, mollusks (the photo below shows one of the representatives of the type) are invertebrate animals. Their soft, non-segmented body is often protected by a shell and consists of three sections: head, trunk and legs. Each of them carries a number of organs.
On the head is a pair of tentacles that serve as the organ of touch. The leg is located on the ventral side of the body, providing movement of the mollusks. The body of animals is surrounded on all sides by a fold of integument called the mantle. As a result, a cavity is formed between this structure and the body. Respiratory organs are located in it, the ducts of the digestive, excretory and reproductive systems open.
Classification Basics
Please note that the mollusks, photos of which are presented in our article, differ significantly in appearance. Depending on these features, three classes are distinguished: gastropod and cephalopods, bivalves. Representatives of the first group mastered not only water bodies, but also various land areas: soil or forest litter. In gastropods, all parts of the body are well developed. The trunk of most of them is located inside a spirally twisted shell.
The body of the cephalopod mollusk consists of a leg and trunk, and the leg is modified into tentacles. A characteristic feature of this class is the ability to reactive movement. 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 reservoirs. They do not have a head; therefore, they also lack parts of organs: tentacles, pharynx, tongue with grater, salivary glands. Their shell consists of two valves, which in most species have protrusions and indentations. Their combination is called a castle.
Digestive system
All mollusks have a digestive system of the through type. In Gastropods and Cephalopods, it begins with a mouth opening. On its border with the throat are the horny jaws. With their help, mollusks scrape food from various surfaces. The anus, which ends this system, opens into the mantle cavity.
The main digestive gland in mollusks is the liver. It is an outgrowth of the middle intestine. Most species have salivary glands. Almost all cephalopods release toxic substances, which paralyze and kill prey.
What is the digestive gland in mollusks
This part of the digestive system is also called the hepato-pancreatic or hepatopancreatic gland. Through specialized excretory ducts, it remains connected with the intestines. The 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 that belong to the cephalopod class? Representatives of this group are characterized by more specialized structures. They separately have a liver, pancreas, and salivary glands.
Food Types: Bivalves and Cephalopods
The structural features of the digestive system of each class of mollusks and the type of their nutrition vary. For example, Bivalves are typical filtrators. To do this, they use special structures called siphons. They are of two types. Water with suspended organic particles flows through the inlet siphon. 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 outlet siphon.
Most cephalopods are predators. On their tentacles are suction cups that help to catch and hold prey. They feed on crustaceans, fish and other mollusks. In the oral cavity of the Cephalopods are a grater and horn jaws. They are so powerful that they can even crush crab shells. To attract prey, these mollusks have special glow organs. And in order to protect themselves from enemies, they use ink glands. When her secret gets into the water, a dark spot forms, under the cover of which the animal hides.
Features of nutrition of mollusks: class gastropods
These mollusks, in a predominant number of cases, are herbivorous. When moving, they scrape off algae with a grater and horn jaws. What is the digestive gland in mollusks of this class, which are predators? In some of these species, sulfuric acid is part of the saliva . It is capable of dissolving the shells of victims or the poison of enemies. Such carnivorous gastropods use graters only to keep prey.
Once in the oral cavity, food particles adhere to viscous saliva. Numerous cilia, which are in the throat, direct this lump into the stomach. At its pointed end is a special structure called prostil. It is formed by sedimentary particles. Prostil acts like a bobbin, separating food particles from saliva.
Surprisingly, salt mollusk feeds. Their digestive system is completely reduced. Scientists suggest that they use chemosynthetic bacteria to absorb food .
So, mollusks are invertebrate animals that have a soft, non-segmented body. They have a digestive system of the through type, as well as specialized glands: salivary, pancreas and liver. According to the method of feeding the mollusks, they can be combined into three large groups: filtrators, herbivores, and predators.