The document summarizes the digestive system of Scoliodon laticaudus (dogfish shark). It describes the major components of the alimentary canal including the mouth, buccal cavity, pharynx, esophagus, stomach, intestine, as well as associated glands like the liver and pancreas. It also discusses the roles of various secretions in digesting the shark's diet which mainly consists of other fish, crabs, and lobsters. The spiral intestine valve increases surface area for optimal absorption of nutrients.

1. Fufal Bhavin M
Sem-3
Roll No:3
Department of Marine Science
M.K.B.U
Digestive System of Scoliodon Laticaudaus

3. The digestive system includes the alimentary canal or gut
through which food passes and glands that open into it.
Alimentary Canal : Alimentary canal beings at mouth and
terminates in anus. It is longer than the body and includes
buccal cavity, pharynx, esophagus, stomach and intestine

4. Alimentary Canal
1. Mouth
2. Buccal cavity
3. Pharynx
4. Oesophagus
5. Stomach
6. Intestine

5. • Mouth – It is a wide crescentic opening on the ventral side of head. It
is bounded by folds of integument sometimes called upper and lower
lips.
• Buccal cavity – mouth opens into a spacious dorso-ventrally flattened
mouth cavity, lined by mucous membrane and bordered by the jaws.
Teeth are not attached to the jaw cartilages, but are simply embedded in
the skin like other placoid scales.
• Pharynx – posteriorly the buccal cavity merges insensibly with the
larger cavity of pharynx lined by endoderm. Either lateral side of
pharynx lined contains an oval pit spiracle and five separate vertical
internal gill-slits of gill pouches.
Alimentary Canal

6. • Oesophagus -pharyngeal cavity narrows down posteriorly into a
short but wide tube, the oesophagus, with thick muscular wall.
• Stomach-the oesophagus passes backwards into the abdominal
cavity to open into a large muscular and U-shaped stomach. It
proximal limb is longer, wider and distensible. It is called the
Cardiac stomach. the distal limb is shorter and narrower and called
the pyloric stomach. At the junction of cardiac and pyloric
stomach is present a small blind outgrowth, the blind sac, as well
as a sphincter valve.

7. • At the end of pyloric stomach is present a strong circular muscle band,
called pyloric valve, guarding its opening into a small but thick-walled
muscular chamber, the bursa-entiana.
• Intestine - Bursa entiana is followed by intestine. It is a straight wide
tube about the diameter of cardiac stomach in the middle of its length.
Its narrow anterior part receives the bile and pancreatic ducts. In
scoliodon, the inner mucous linning of intestine becomes folded
anticlockwise into a longitudinal spiral or scroll of about two and half
turns. This is called the scroll valve or spiral valve. The last part of
intestine is called rectum. It is a shot and narrow tube opening behind
through anus into the ventral cloaca. A small finger-like caecal or
rectal gland of unknown function opens dorsally into the rectum.

8. Glands of alimentary canal
1. Liver
2. Pancreas
3. Caecal or rectal gland
4. Spleen

9. Glands of alimentary canal
• Liver- liver of dogfish is a massive yellowish bilobed gland. The
two lobes extend backwards freely into abdominal cavity, but they
are united anteriorly and attached to septum transversum by a
ligament. A V shaped thiin-walled gall bladder. Bile duct receives
branches from the lobes of liver. Liver secretes bile, stores
glycogen and fat, and destroys worn out erythrocytes of blood.
• Pancreas- it is a compact, whitish or pale bilobed gland consisting
of a longer dorsal lobe running parallel to the posterior part of
cardiac stomach and a smaller ventral lobe closely applied to the
pyloric stomach.

10. • Caecal or rectal gland- It is a small finger-like body attached by its
duct to the dorsal side of rectum into which it opens. It has a central
cavity lined by cuboidal epithelial cells.
• Spleen – it is a large gland closely attached like a fringe to the
cardiac and pyloric stomachs. But it has no physiological relation
with alimentary canal and functionally associated with circulatory
system. It is lymphoid organ which produces lymphocytes.

11. Food and physiology of digestion
• Scoliodon is predaceous carnivore, feeding mainly on other fishes.
Its diet may also include crabs, lobsters and worms. food is
swallowed without mastication. No digestion occurs in buccal
cavity which lacks salivary glands.
• The gastric juice in stomach contains pepsin and hydrochloric acid.
It converts proteins into syntonin, proteoses and peptones, but
cannot digest chitin.

12. • Bile make the semi digested food alkaline in intestine
while pancreas secretes trypsinoge, amylopsin and lipase
for digestion of proteins, starches and fats, respectively.
• Scroll valve in intestine serves to retard the passage of
food and affords a large surface for absorption of the
products of digestion.