Anatomy of finfish and shellfish

Unit 13 - Mollusca

13.3.4. Digestive System
Alimentary canal
The mouth leads into a hard and round muscular pharynx or buccal mass, containing a pair of horny jaws and an odontophore with a radula. The jaws resemble an inverted parrot's beak and are moved by strong muscles. The slender oesophageous leads from the buccal mass through the liver to the large, sac-like and thick walled muscular cliverticulum stomach, closely connected with a complex valve in between. The stomach is followed by a short intestine, demarcated by a constriction from the rectum, which terminates in the anus at the base of the siphon. Two anal valves of doubtful function are attached to the sides of the anus.

Fig. 5- Loligo Alimentary canal

Digestive glands
The salivary glands, two in the dorsal muscular wall of the pharynx, and one embedded in the ventral end of the liver, open by their ducts into buccal cavity. The liver is a single, median and cone-shaped organ with its broad base near the collar. The pancreas is a small V-shaped struc¬ture lying anterior to the stomach. A single hepatopancreatic duct from the liver and pancreas leads into the caccum.
Food and feeding mechanism
The squid is carnivorous, feeding on small fish, Crustacea, Mollusca and other squids. The two long tentacles, each of which is retractile into a pouch of the head, can extended forward to seize the prey, when at a distance, by their suction cups and draw it towards the mouth, where it is held firmly by other arms. The jaws cut large pieces which are swallowed rapidly, the small radula probably seldom used.
Digestion
The food is partially digested in the stomach by digestive fluids or liver and pancreas. In the caecum, digestion is completed and absorption takes place. The indigestible food passes on to the intestine and expelled thr9ugh the anus.