1. Department of Zoology and Environmental Sciences
LACHOO MEMORIAL COLLEGE OF SCIENCE & TECHNOLOGY
[AUTONOMOUS] JODHPUR (RAJASTHAN)
By
Bharat Gander
M.Sc. I Semester
SEMINAR PRESENTATION 2016

3. SYNOPSIS
o The Annelida
o Digestive system in nereis
o Classification of nereis
o Digestive system
1. Alimentary canal
a) Forgut
b) Midgut
c) Hindgut
2. Histology of alimentary canal
3. Food
4. Feeding Mechanism
5. Digestion

4. THE ANNELIDA
 Segmented worms make up the Phylum Annelida. The phylum
includes earth worms and their relatives, leech, and a large
number of mostly marine worms known as Polychaetes. Various
sps of Polychaete are known as lugworms, clam worm bristle
worm, fire worms and sea mice.
 Annelida can be told but their segmented bodies. Polychaetes
have, predictably, many bristles on the body while earthworm and
leeches have fewer . There are about 1500 species of annelid know
today 4

5. DIGESTIVE SYSTEM IN NEREIS

6. CLASSIFICATION OF NEREIS
Phylum – Annelida
Class - Polychaeta
Sub class - Errantia
Family - Nereidae
Genus - Neanthes or Nereis

7.  Commonly called as Rag worm or Clam worm & is the simplest
Annelid.
 Examination of preserved specimen shows Cylindrical and
Elongated body from which is divided into similar Metameres
or Segments (Importend Evolution) about 200 in number.
 Mouth is found on the anterior surface of the Peristomium.
 Body segments, except head & anal segment, contain each pair of
locomotion Parapodia.
 Organ grade system present.

8. Fig - Nereis - Anterior end of body in dorsal view

9. DIGESTIVE SYSTEM
 It Contain Of The Alimentary Canal And The Associated Digestive Glands.
1) Alimentary Canal – The alimentary canal is a long & straight tube running from mouth to
anus, although its diameter varies in different region.
 The interesegmental coelomic septa and the mesenteries hold the alimentary canal in position.
 On the basis of its lining the alimentary canal is differentiated into three regions :
 STOMODAEUM or FOREGUT, internally lined by ectoderm and cutical and comprising buccal
cavity and pharynx.
 MESENTERON or MIDGUD, internally lined by endoderm and comprising oesophagus and
stomach- interstine.
 PROTODAEUM or HINDGUT , internally lined by ectoderm and cuticle and comprising rectum.

10. A. FOREGUT- The mouth is a transversely elongated slit located ventral
to the prostomium and bordered by the peristomium .
 It opens into a wide chamber, the buccal cavity situated inside the
peristomium.
 The buccal cavity leads behind into muscular pharynx, extending up
to the 4th segment. both the buccal and pharyngeal region are
surrounded by severak muscular a single muscular coats to form
apparently a single muscular organ, the Buccopharyngeal region .
 The cuticle lining the buccal and phayngeal cavities is specially
thickened at various spots to form small dark brown denticles or
paranaths, which are regularly arranged .

11.  The cavity of the pharynx is narrow and its posterior part is
greatly muscular and thick–walled with a pair of large, powerful,
dark, movable, chitinous and laterally placed jaws, embedded in
it. Each jaw has a posterior round hollow base, embedded in
muscles, and an anterior, pointed, solid, incurved and sligntly
notched apex, projecting into the lumen of pharynx.
 The inner margin of each jaw bears several strong serrations or
teeth.
 The whole of buccal and pharyngeal regions can be turned inside
out, while feeding.

12. B. MIDGUT - The pharynx opens posteriorly into a short and narrow
oesophagus followed by the stomach-interstine.
 In most species, the oesophagus runs up to 9th segment . A pair of large
unbranched sacculated, laterally placed glandular pouches, called the carca
or orsophageal glands, which probably secrete digestive juices open into
oesphagus.
 The passage of food is ragulated by a sphincter muscle present at the
posterior end of the oesophagus. The stomach –intestine, which is
segmentally constricted the remaning length of the body. A typhlosole is
absent.
 The food moves in it by peristalsis, a series of progressive waves of
alternating contractions of the circular and longitudinal muscles.

13. C. HINDGUT - The rectum, lying in the last body – segment or pyguduum,
opens posteriorly through the terminal anus to the outside.
2. Histology of alimentary canal – The wall of the alimentary canal consist
from the outside of (i) the visceral layer of coelomic epithelium. (ii) a layer of
longitudinal muscle fibers, (iii) a layer of cutical in buccal cavity and
pharynx.
3. Food – Neanthes is said to have a carnivorous dirt, feeding on small
Mollusca, Caustacea, sponges and other animals, which it seizes by means of
everted jaws and the denticles. Sometimes it may be found between the
valves of an empty clams, but actually it eats much smaller animals. Many
species also feed upon algee,sich as Fucus or Ulva.

15. 4. Feeding Mechanism – The worm lives in the burrow with its hea and the
anterior part of the body protruding slightly. When small animals venture too
close, the worm suddenly everts its heavily armed pharynx to seize the prey.
In eversion, the buccal cavity and the pharynx turn inside out and protrude
through the mouth in the form of an or proboscis.
 The two pharyngeal jaws are thust firth widely and, on retraction, they come
close together grasping the prey,which is dragged inside the burrwo and then
swallowed by with drawing the pharynx
 Eversion of the introvert is brought about partly by the contraction of the
protractor muscles, running backwards and inwards from the peristomial
wall to the buccal cavity and phatungeal wall, and partly by the pressire of the
coelomic fluid.

16. Fig: Diagramatic representation of the action of “Introvert in nereis
(i) introvert at rest (ii) Introvert protruded

17.  The extent of ecersion is determined by the position of muscular diapharagm
stretching from the buccal cavity to the body- wall of the first segment
 The retraction or invroversion is effected by the contraction
of the strong of the strong retractor muscles running forward from the body-
wall to be inserted into the hinder end of the pharynx
5. Digestion – The food is pushed onward inside the gut by peristalsis caused
by muscles producing a succession of rhythmic waves of constractions along
the gud –wall.
 Digestion is extracellular occuring mainly in the stomach- interstine, where
the enzyme producing by the oesophageal glands and the glands of the
digested food also occurs here by diffusion through enteric epithilium into the
blood of the gud capilalaries.

18.  The undigested part of the food passes on to rectum and
egested through the terminal anus situated on the posterior
end of the anal segment.