Phylum annelida, Biology

PHYLUM ANNELIDA

Definition  and Introduction

Bilateral and  protosomial  eucoelomate  eumetazoans  whose  long   narrow and  wormlike body  is division  into  ring like  true  or metameric segments (Gr. Annelus= little  ring) and the skin  usually bears  enjointed  chitinous appendages , termed setae.

Commonly  known as segmented worms. About 9,000 species known.

Brief History

Linnaeus (1758) included all  soft  bodied worms  in Vermes  Lamarck (1801)  established phylum  Annelida for higher types   or worms.

Important Characters

1.       Annelids  occur  widely in water  or moist soil. Some  free living  some  burrowing  and  a few parasitic.

2.       Body  usually long , slender and  distinctly segmented. Body  cavity ( coelom and many internal organs also exhibit  metameric segmentation .

3.       Soft  and extensile body  triploblastic  and bilateral.

4.       Muscular and  contractile  body wall  covered  by a thin moist cuticle containing secreted unjointed  chitinous  setae. A distinct columnar epidermis  and both  longitudinal and circular muscle layers  present.

5.       Body  cavity is true coelom lined  by sesodermal epithelium ( peritoneum)  phylogentically,  annelids are, perhaps, the  first animals to acquire a ture  schizocoelic  coelom, In most  annelids ,it is divided into segmental  chambers  by inter segmental septa. Coelomic fluid  contains  cells ( corpuscles ) .

6.       Alimentary  canal  straight  with  anterior  mouth  and posterior  anus .Due to spacious, fluid  filled  body cavity  between  body  wall and  alimentary  canal, the  body  grossly  appears  like a tube within  a tube  in section.

7.       A distinct and    closed type  of blood vascular system present. Blood of red  colour with haemoglobin  dissolved in plasma. Free amoeboid  blood  corpuscles  present, but  no red  blood  corpuscles.

8.       Respiration  through moist skin some  possess gills.

9.       Excretion  by minute  and coiled paired tubules  of ectodermal  origin ,called  metanephridia.

10.      Nervous  system uncludes nerve ring  near anterior end. Two  ventral nerve  cords  extending throughout body length   from nerve ring, and  segmental ganglionic  swellings upon  nerve cords, representing true  metamerism. Several types  of sensory  cells  and organs found.

11.   Sexes  separate  or united .Reproductive  organs  develop  from  coelomic  epithelium.

12.   Development  mostly direct. When  present , the larval  stage is trochophore.

Posted Date: 10/4/2012 2:58:15 AM | Location : United States







Related Discussions:- Phylum annelida, Assignment Help, Ask Question on Phylum annelida, Get Answer, Expert's Help, Phylum annelida Discussions

Write discussion on Phylum annelida
Your posts are moderated
Related Questions
Peroxisomes and Glyoxisomes A number of metabolic reactions, such as, the oxidation of amino acids and lipids result in the production of hydrogen peroxide. As hydrogen peroxid

Q. How different are hemoglobin and oxyhemoglobin? Where is it expected to find a higher concentration of oxyhemoglobin, in peripheral tissues or in the lungs? Oxygen-bou

What is the primary energy source for life on earth? The primary energy resource for life on earth is the sun. The sun plays the vital role of keeping the planet warmed and it

Echocardiography: LV hypertrophy can be identified using M-Mode and 2 D imaging. Indications of myocardial ischemic states and systolic functions can be assessed by studying region

List specific reasons why the inflammatory response is considered a body defense mechanism.

Q. Explain about Low blood sugar? Low blood sugar can also be caused by accidentally taking too much of insulin. When this occurs, more insulin is present in the body than nee

Q. Explain Diseases of pericardium? Pericardium is the sac covering the heart. Pericardium consists of two layers-the visceral pericardium (epicardium) and the parietal pericar

A 19 year old model for Glamour magazine tripped over an extension cord causing injury to her epidermis. She is afraid the injury will leave a scar. Based on your knowledge of rege

What are the Advanced surgical procedures The scope of implantology has widened to include many more clinical situations which would be hitherto contraindicated for implants du

WHAT IS SYMBIOTIC THEORY. PLEASE EXPLAIN THIS TO ME IN A VERY SIMPLE WAY.