Himalaya Ahmed HimuSession : 2012-2013

Institute of Marine Sciences and Fisheries

University Of Chittagong

Basic Concept Of Annelida

Aquatic,marine or fresh water species

Triploblastic,coelomate

Bilaterally symetrical

Segmented metazoa

Body:covered by thin cuticle

Body:Metamarically segmented

Appandages:Unjointed(when present)

Vascular system:Closed

Blood:Red

Respiration:through body or gills

Digestion:Extracellularly

Reproduction:Asexualy

Nervous system:Brain or paired preoral genetic

Class: 4 class-1.Polychatae Marine & carnivorus Body:Elongated & segmented Clitellum:Absent Reproduction:Asexual Excretory organ:paired nephredia

Example-Nereis virens

.Archioligochatae

.Neoligochatae

3.Hirudinia: Ectoparasitic & Fresh water forms

Body:Elongated,flattened,cylindrical

Parapodia & Setae:Absent

Reproduction:Sexual

.Acanthobdellida

.Rhynchobdellida

.Gnathobdellida

4.Archiannelida: Marine forms

Body:Elongated & worm like

Satae & parapodia:Absent

Larvae:trochophore

Prostodium:bear 2 or 3 tentacles

Systematic position:

Phylum:Annelida

Class:Polychatae

Order:Errentia

Family:Nereididae

Genus:Neanthes

Species:Neanthes virens

Finding:Sea shore,under the stones ,sea weeds

Lives in:Tubular,u-shaped barrows in sand or mud at tide level

Feeds on:Small insect,mollusks & worms

Very active in night & passive in day

During breeding period it leaves the borrow

Shape & Size:

.Body:Long,narrow,bilaterally symmetrical,

Tapering posteriorly & broad anteriorly.

.Length:Range from 30 to 40 cm.

. Width:2 to 6 mm in width.

Colouration:N virens-Bluish,N limnicola-Brownish,N dumerilli-Reddish,N cultrifera-Greenish

Distinct head & the rest of the body is divided by a series of ring like narrow grooves

The number of metameres varies from species to species

Divition of the body:

The boy of N. is divisible into 3 parts-

.Heads

.trunk &

.Pygidium

Distinct,prominent & well developed

Consists of 2 main parts-

.Prostomium

.Peristomium

Trunk:• Posterior to the head

• Metamarically segmented

• Segments are known as metameres or somites

The last segment that’s called tail Bears no parapodia Havibg a pair of elongatd anal cirri

Parapodia :

Each segment of the body Except peristomium & anal segment Flat,fleshy,hollow & vertical flap like Huxley first named these

The body wall has 4 parts-1.cuticle:• Thin ,tough,chitinous & Non-cellular• Performed by numerous pores• Opening to the epidermal gland cells2.Epidermis/Hypodermis:• Below the cuticle• Composed of columnar epithelial cells• Near the base of partapodia• Thick,richly vascularized• Helps in respiration

Below the epidermis

3types muscles-circular,longitudinal & oblique

Concentration of these muscles make the body longer & thinner

Function:To react the parapodium

Muscles layers are syncytial tissue

Mainly carnivorus Feeds on small animal crustaceans,mollusks,sponge Larvae & other worms and animal

Feeding mechanism:o captured by the eversion of buccal cavity &

protrusion of pharynx.o Pharynx brings out the jaw in front to grasp

the prey.o Buccal cavity is everted due to pressure of

coelomic fluid.

***Alimentary canal:

Straight & unbranched tube

From mouth to anus

Having 2 openings to the exterior

1.anterior:Ingested food

2.Posterior:Undigestedfood remains are removed.

Transverse slit

Lies ventral to the prostomium

Bordered:Ventrally & laterally by prostomium

Opens into the buccal cavity(wide chamber)

2.Buccal cavity :

.Short but wide

.Situated:Inside the prostomium

.Leads into pharynx

Middle regions of alimentary canal

Consisting:Oesophagus & stomach intestine

Lined internally by endoderm

1.Oesophagus:

.Narrow shape

.Secret digestive enzymes

Principle site of digestion & absorption

Opens into rectum in last segment

A distinct stomach is, however,not found

***Proctodium:

.Posterior part of alimentary canal

.Lined internally by ectoderm &cuticle

.Consisting:Rectum

Short,tube-like structure

Lying in the anal segment

Opens posteriorly through the terminal anal

Excretory organ: Coiled tube-like nephredia

Structure of nephredia:Each nephredia has an oval syncytial mass of

protoplasm containing a long,ciliatedcanal,the nephredial tubule.The syncytialprotoplasm is differentiated into a body & nick.The main body is an irregular,oval,compact gland-like mass directed ransverse lying the segment.

Neanthes are- Diocious(sexs are separate) Gonads are neither permanent nor distinct Gonads developed during the breeding

season Male gonad is tests,female gonad is

overies

Gonad:.Formed by coelomic epithelium.Male tests extend in many segmens

.Mixonephredia act both as excretory & genetial ducts

Dorsal ciliated organs:

.A pair of dorsal ciliated organ

.Small,much folded,funnel-shaped

.Opens into the coelom by a wide opening

.It has no external opening

.Its nature is still unknown

Neanthes Heteroneanthes

Live in borrows,understones,at the bottom of the sea

Swims at the surface of the sea

Eyes are small & indisti8nct

Prominent,enlarged & highly sensitire to light

Body is not differentiated into region

Differentiated into regions

Neanthes Heteroneanthes

Live in borrows,under stones at the bottom of the sea

Swims activity at the surface of the sea

Eyes are small & undistinct Prominent,enlarged & highly sensitire to light

Body isn’t differentgiatedinto regions

Differentiated into regions

Sexually immetured Mature

All parapodia are alike

Dorsal & ventral cirrus are short

Satae normal,pointed at the tips

Atoke & epitoke Well enlarged

Oral-shaped & arranged fan like toprovideeffective swimming