Scoliodon

2. Dr. Savita Yadavrao Waghmare
T. Y. B. Sc.(Zoology)
Subject :- Chordate III
Topic :- Digestive System Of Scoliodon
Department of Zoology
Dhanaji Nana Mahavidyalaya, Faizpur

3.  The Digestive System of Dog fish or
Scoliodon

4.  Digestion is the process of simplification of
the complex food material, which can be
absorbed and assimilated by the body.

5.  Digestive system consists of alimentary canal
and associated glands.

7.  It is complete and is divided into buccal
cavity, pharynx, oesophagus, stomach,
intestine and rectum. The stomodeal portion
is lined with ectoderm. The mesodaeum is
lined with endoderm. The proctodaeum is
also lined with ectoderm.

8.  It is a semioval slit bounded by upper and
lower lips and is present at the ventral side.

9.  It is a wide cavity containing sharp pointed
backwardly directed homodont and
polyphyodent type of teeth. These are
mainly used merely to prevent the escape of
prey. The mucous membrane is raised to
form the tongue which is glandular and
muscular.

10.  It is a large wide chamber which opens
through five vertical slits called internal
gillslits which open into gills. The mucous
membrane contains numerous denticles to
prevent the escape of prey.

11.  The pharynx opens into a short narrow thick,
muscular oesophagus containing rugae. It
remains closed, except during swallowing of
food, to check the entry of water into
stomach. It opens into stomach, through
oesophageal valve.

12.  It is ‘J’ shaped bent tube which is divided into two parts.
 (a) Cardiac Stomach: It is a long, broad muscular part containing
longitudinal folds. At the end there is a cardiac valve.
 (b) Blind Sac:
 At the end of cardiacs stomach starts there us a small, outgrowth
called blindsac of unknown function.
 (c) Pyloric Stomach:
 The distal limb of stomach starts from cardiac valve and is a short
narrow tube. IT is lined with smooth, mucous membrane with few
longitudinal folds. It ends at the pyloric valve.
 (d) Bursa entiana :
 At the distal end of pyloric stomach a small globular, muscular sac
is present containing continuation of longitudinal folds of pyloric
stomach is called Bursaentiana.

13.  It is a straight wide tube which is divided into duodenum
and ileum.
 (a) Duodenum:
 It is the narrow, anterior part. It receives common bile
duct or ductus choledochus dorsally and pancreatic duct
ventrally.
 (b) Ileum :
 The rest part of intestine is called as ileum. The mucous
membrane is produced into scroll valve. One edge if the is
valve is attached to the intestinal mucosa. But the other
end roles up spirally in anticlockwise manner upto two and
half turn. The scroll valve increases the inner absorptive
area. The passage of food slows down in scroll valve to
ensure proper absorption.
 The intestine is not connected with mesentery and is
opened into the rectum.

14.  It is a short narrow straight tube suspended
by mesorectum. In between ileum and
rectum there is rectal valve containing
circular muscles. It receives rectal gland
which is similar to medulla of kidney and
excretes excess salts. Rectum leads to
cloaca.

15.  It is a short terminal chamber, which receives
ducts of urinogenital system. It has a pair of
abdominal pores.
 Cloacal aperture :
 It is a small longitudinal aperture present
between two pelvic fins.

16.  Liver is a large yellowish two lobed gland
present in between stomach and is
suspended by falciform
ligaments,gastrohepatic omentum and
hepatoduodenal ligament. The V-shaped gall-
bladder stores bile and drains by cystic duct
which fuses with hepatic duct to form
common bile duct. It opens into deudenum.

17.  It is an elongated, whitish gland present
between two limbs of the stomach. It is
divided into two lobes. The dorsal lobe is
present parallel to the posterior part of the
cardiac stomach and ventral lobe, closed to
the pyloric stomach. The pancreatic duct
opens into the ventral wall of the duodenum.

18.  4. Gastric glands:
 These are present in the stomach.
 5. Intestinal gland:
 Numerous microscopic glands of intestine
secrete succusentericus.
 6. Mucous glands:
 Mucous glands are found in the inside
alimentary canal which helps to dissolve the
food and makes the passage slippery.

19.  Food: It is carnivorous, feeding on
crustecian, annelids and small fishes. It is a
voracious feeder and can smell the food from
a long distance.
 Feeding: Due to ventral position of mouth it
has to turn to one side to capture the prey.
The lower jaw is opened by coraco
mandibular muscles. The escape of struggling
prey is prevented by backwardly directed
teeth. Without mastication it is swallowed.

20.  1. Stomach:
 The gastric juice contains pepsin along with
HCl to convert proteins into peptone and
proteoses.
 2. Duodenum:
 The food in duodenum is acted upon by bile
and pancreatic juice trypsin and amylopsin
digest protein and starch but lipase with the
help of bile digests fat.

21.  Absorption:
 The spiral valve extends to the area of
absorption and slows down the passage of food
or absorption.
 Assimilation:
 Due to large supply of food, little storage is
seen. Glycogens and oils are temporarily
stored in the liver cells.
 Egestion – The waste material are thrown out
through cloacal aperture as faeces.