Department of Zoology and Environmental SciencesLACHOO MEMORIAL COLLEGE OF SCIENCE & TECHNOLOGY

[AUTONOMOUS] JODHPUR (RAJASTHAN)

DIGESTIVE SYSTEM IN ANNELIDA

ByBharat Gander

M.Sc. I Semester

SEMINAR PRESENTATION 2016

DIGESTIVE SYSTEMIN

ANNELIDA

SYNOPSISo The Annelidao Digestive system in nereiso Classification of nereiso Digestive system

1. Alimentary canala) Forgut b) Midgut c) Hindgut

2. Histology of alimentary canal3. Food4. Feeding Mechanism5. Digestion

THE ANNELIDASegmented 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

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DIGESTIVE SYSTEM IN NEREIS

CLASSIFICATION OF NEREISPhylum – Annelida

Class - Polychaeta

Sub class - Errantia

Family - Nereidae

Genus - Neanthes or Nereis

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.

Fig - Nereis - Anterior end of body in dorsal view

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.

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 .

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.

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.

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.

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.

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

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.

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.

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