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The digestive system of gastropods (slugs and snails of every kind) has evolved to suit almost every kind of diet and feeding behavior. Gastropods as the largest taxonomic class of the mollusca are very diverse indeed: the group includes carnivores, herbivores, scavengers, filter feeders, and even parasites. In particular, the radula is often highly adapted to the specific diet of the various group of gastropods. Another distinctive feature of the digestive tract is that, along with the rest of the visceral mass, it has undergone torsion, twisting around through 180 degrees during the larval stage, so that the anus of the animal is located above its head. A number of species have developed special adaptations to feeding, such as the "drill" of some limpets, or the harpoon of the neogastropod genus ''Conus''. Filter feeders use the gills, mantle lining, or nets of mucus to trap their prey, which they then pull into the mouth with the radula. The highly modified parasitic genus ''Enderoxenos'' has no digestive tract at all, and simply absorbs the blood of its host through the body wall.〔 The digestive system usually has the following parts: * buccal mass (including the mouth, pharynx, and retractor muscles of the pharynx) and salivary glands with salivary ducts * oesophagus and oesophagal crop * stomach, also known as the gastric pouch * digestive gland, also known as the hepatopancreas * intestine * rectum and anus ==Buccal mass == The buccal mass is the first part of the digestive system, and consists of the mouth and pharynx. The mouth includes a radula, and in most cases, also a pair of jaws. The pharynx can be very large, especially in carnivorous species. Ducts from large salivary glands lead into the mouth, and the oesophagus also supplies the digestive enzymes that help to break down the food.〔 Many carnivorous species have developed a proboscis, containing the oral cavity, radula, and part of the oesophagus. At rest, the proboscis is enclosed within a sac-like sheath, with an opening at the front of the animal that resembles a true mouth. When the animal feeds, it pumps blood into the proboscis, inflating it and pushing it out through the opening to grasp the gastropod's prey. A set of retractor muscles help pull the proboscis back inside the sheath once feeding is completed.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「digestive system of gastropods」の詳細全文を読む スポンサード リンク
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