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Prawns are small aquatic crustaceans, some of which can be eaten as well. The digestive system of prawns is divided into the alimentary canal and digestive glands. Let us study them separately.

Alimentary Canal

The alimentary canal of prawns is divided into the foregut, midgut and hindgut.

Foregut

The foregut, also known as the anterior alimentary canal, includes four parts:

• Mouth Opening: It is the opening situated at the ventral side of the head though which food enters. It is a big opening that lies between the 3^rd and 4^th cephalic segments.
• Buccal Cavity: It is a small flattened chamber found between the mouth and oesophagus. The food is crushed in this part.
• Oesophagus: It is a vertical broad tube that runs between the buccal cavity and stomach. It has a muscular inner lining and has four longitudinal folds.
• Stomach: It is a large sac-like organ that is situated behind the oesophagus. It is divided into two parts: the cardiac stomach and pyloric stomach.
• Cardiac Stomach: It is the anterior portion of the stomach. It has inner cuticular walls that are lined with minute bristles. The wall of the cardiac stomach has the following plates – a circular plate situated in the anterior portion, a lanceolate plate in the dorsal side of the posterior portion and a hastate plate that is found in the mid-ventral portion.

Each ridged plate has multiple rows of comb-like setae, also known as comb plates. The hastate plate functions to cut and grind the food.

• Pyloric Stomach: The cardiac stomach opens into the pyloric stomach by an X-shaped cardio-pyloric opening. This opening has four valves – one posterior, one anterior and two lateral valves. The posterior valve is the fold of the stomach wall, the anterior valve is the extension of the hastate plate and the two lateral valves are extensions of the guiding ridges.

This portion of the stomach is incompletely divided by folds into a large ventral chamber and a small dorsal chamber and is much smaller than the cardiac stomach. The digestive gland, hepatopancreas, opens into the ventral chamber.

Midgut

The midgut or the middle alimentary canal is a long, narrow and tube-like structure that begins from the dorsal chamber of the stomach and runs till the 6th abdominal segment. It has longitudinal folds, thus making the lumen of the tube narrow.

Hindgut

The hindgut or the posterior alimentary canal is composed of two parts:

• Rectum: It is the last portion of the intestine that is swollen and muscular. It has a number of internal folds.
• Anus: It is a slit-like aperture through which the alimentary canal opens into the exterior. The faecal waste is eliminated from this aperture.

Digestive Glands

The digestive gland of the prawns is hepatopancreas that serves the purpose of liver, intestine and pancreas of higher animals. It is an orange coloured, bilobed organ that circles the entire pyloric stomach.

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Also Read:

• Palaemon: Diagram and Characteristics
• Difference between Crustaceans and Molluscs
• Phylum Arthropoda – Characteristics & Classification