Digestive system of pila
- 1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai Digestive system of Pila Dr. Sonia Bajaj (Head of Department)
- 2. Introduction- • It is commonly called “apple snail” and is found in fresh water ponds, pools and ditches in India and adjacent regions. • Shell is external and spirally coiled and is comprised of 6 whorls. • The axis around which coiling takes place is known as columella, the top whorl is known as apical whorl and the large and ultimate whorl is known as animal chamber. • The animal chamber is covered over by operculum. • Along the animal chamber runs a vertical groove the varix, which connects the penultimate whorl and inner lip of mouth. • The animal comprises a head, foot and a visceral mass. • Foot is muscular, flat and serves for creeping. • Visceral mass consists of main body organs and is spirally coiled. • Kidney and ctenidium (gill) unpaired. • A part of mantle is modified into pulmonary sac and serves for aerial respiration. The other mode of respiration being aquatic. • Sexes are separate and animal is herbivorous.
- 3. Digestive system- In the digestive system of pila a long coiled alimentary canal and digestive glands are present. The alimentary canal will show the following parts. A.-Alimentary Canal: • It is a coiled tube extending from the mouth and terminating at the anus. It has three regions, the • Fore gut comprising of buccal cavity and oesophagus, • Midgut including stomach and intestine • Hindgut consisting of rectum. • Mouth: At the anterior end of the head mouth is present. It opens into buccal cavity. • Buccal cavity: Mouth leads into buccal cavity which is lined by cuticle and surrounded by a large, thick walled, highly muscular structure, called buccal mass.
- 4. Buccal Mass: The mouth leads into a large cavity of buccal mass or pharynx having thick walls with several sets of muscles. Vestibule and jaws: • Anterior tubular part of buccal cavity is called vestibule. The posterior part of the vestibule is marked by a pair of jaws, connected by a thin cuticular membrane. The jaws bear muscles and their anterior edges have teeth-like projections for cutting up vegetable food. It shows jaws and radula On the floor of the buccal cavity odontophore is present. On this odontophore radula moves. Odontophore: • The posterior part of the buccal cavity forms, on its floor, a muscular tongue or odontophore. Odontophore is supported by two sets of cartilages . • (i) A pair of more or less triangular superior cartilages at the top of the odontophore. • (ii) A pair of S-shaped lateral cartilages lying on the sides of odontophore.
- 5. Radula - • On the floor of buccal cavity lie a chitinous curved, ribbon-like structure called the radula or lingual ribbon, its anterior end bearing a pair of wing-like flaps lying over the odontophore, while posterior end lodged in radular sac flexed behind and below the buccal mass. • Radula itself is formed by secretion of the epithelial lining of the radular sac. Below the radula lies a delicate and elastic sub-radualr membrane. Dorsal surface of the radula bears teeth arranged in numerous transverse rows. Each row contains 7 teeth, one central (rachidium) and one lateral and two marginals on its either side giving the formula 2,1,1,1, 2. • The chain-saw movement of radula on the odontophore makes it an efficient organ for rasping of food particals. • The wear and tear of anterior part of the radula is maintained by regular addition of new material at its posterior end. It works like a rasping organ. With the help of this organ pila will cut the food into bits.
- 6. Oesophagus: Buccal cavity opens into oesophagus. It is long tube. At the junction of oesophagus & buccal cavity two oesophageal cavities are present. They show salivary glands. 4) Stomach: Oesophagus opens into stomach. It is brown coloured sac like structure. It is divisible into two parts. Anterior part of the stomach is connected with oesophagus. Around this digestive glands are present. The posterior part of stomach is called pyloric stomach. It shows a blind caecum. Intestine: •Behind the stomach a long and coiled intestine runs backwards into the viscera to join the rectum. Rectum: •It comprises of thick walled tube which extends into the branchial chamber of the mantle cavity between the ctenidium and genital duct. It opens outside through anus..
- 7. Digestive Glands : • Buccal glands • Salivary glands • Digestive gland (or) Hepatopancreas. Buccal glands: In the buccal cavity wall these glands are present. They secrete a juice whose function is not clearly known. Salivary glands: They are present in the two oesophageal cavities. They give salivary ducts. They open into buccal cavity. The enzyme present in this saliva will digest the carbohydrates. Digestive gland /Hepatopancreas: It is a big gland. It is brown in colour. It occupies bigger part of the visceral mass. In this gland three types of cells are present. They are a) Secretory Cells: They secrete digestive juices. b) Intracellular digesting Cells: These cells will perform intracellular digestion. c) Calcium Cells: These cells will store calcium phosphate. Salivary gland Digestive gland
- 8. Feeding Mechanism- Digestion 1: Pila takes smaller plants and their leaves as food. With the help of walls of Buccal cavity it will catch the leaves. Radula will cut the leaves into bits. In the buccal cavity this food is mixed with saliva. Digestion 2: The soft food will enter into stomach. The enzyme present in the saliva will digest the carbohydrates. The digestive juices produced by the secretory cells of the hepatopancreas will digest the food in the stomach. Partly digested food particles will be taken by the cells of hapatopancreas and the digestion is completed in these cells. It is called intracellular digestion. The undigested food will be sent out of the anus. Thus, both extracellular and intercellular digestion occur. The stomach is the site of extracellular digestion and the digestive gland is the site of intracellular digestion and absorption, this is characteristic of Mollusca. Absorption of digested food takes place mainly in the digestive gland and some in the intestine.
- 9. References- Modern text book – R.L.Kotpal Jantu Vigyan- S.M. Sexsena Jantu Vigyan- Dr.H.N. Baijal