Annelida- General Characters and classification

Introduction
General characters
Classification

1. Bollapalli Ashok Kumar M. Sc ., B.Ed.,M.A (Lit)CSIR-NET,( Ph.D ) LECTURER IN ZOOLOGY KRK Govt Degree & PG College ADDANKI-523201 Phone:[phone] Email: [email protected] Annelida

2. INTRODUCTION-ANNELIDA Annulus= Ring (Latin) Body is divisible into Rings Annelids grouped in Vermis in Early days 1798- Cuvier separated them from Unsegmented worms Lamarck First used the term Annelida Earlier, Scientists believed Annelida evolved from Unsegmented worms But Sedgwick believed , Annelids evolved from the animals with undulating movements during which process the body became segmented

3. General characters- ANNELIDA Land and water dwelling-marine, fresh watered, few ectoparasites Bilaterlally symmetrical Lives in burrows/ build tubes First true coelomates- tube inside tube body plan. Coelom lined by peritoneum, Space filled with fluid, acts as Hydraulic skeleton, in leeches space is filled with Botryoidal tissue Triploblastic animals- three germ layers- Ecto , Endo and Mesoderms

4. General characters- ANNELIDA True segmentation- external and internal, through grooves and septa respectively Each segment is called a metamere and the segmentaion is metameric Body covered by Cuticle derived from Epidermis , protective in function Body wall is dermo - muscular with longitudinal and transverse muscles Locomotion – setae- chitinous bristles, Parapodia Alimentary canal tubular with mouth and anus with associated glands, extracellular digestion

5. General characters- ANNELIDA Closed blood vascular system, blood red in colour due to Haemoglobin/ Erythrocrourin , in dissoved state, Amoeboid cells in Plasma No special respiratory organs, cutaneous respiration except in Arenicola Gills help in respiration Excretion through nephridia , coiled ectodermal tubes, urea – semi terrestrial animals, Ammonia- aquatic animals, Ureotelic / Ammonotelic Nerve ring- suprapharyngeal , sub pharyngeal ganglia, double ventral nerve cord, segmental ganglia

6. General characters- ANNELIDA Cephalisation – head with sense organs like eyes and tentacles Gonads- mesodermal in origin, either hermaphrodite or unisexual, fertilisation is external /internal Spiral cleavage but cleavages are Holoblastic Development is direct/ indirect with trochophore

7. Classification - Annelida Annelida is divided into three classes. They are

8. Class : POLYCHAETA( Poly= Many; Chaetae= Setae) Marine- Bottom dwelling/ planktonic forms More cephalisation with eyes , palps and tentacles Clitellum is absent Numerous segments and distict Locomotion – Parapodia / lateral feet- biramous in structure Sexes separate, more gonads develop during breeding, gonoducts are absent Development indirect- Trochophore larva Burrowing/ tube dwelling, bioluminiscent

9. Class : POLYCHAETA( Poly= Many; Chaetae= Setae) Divided into two sub classes Errantia Sedentaria Sub Class Errantia : ( Errars = Wandering) Sl No Example Common name 1 Neanthes ( Nereis ) Rag worm/ Clam worm 2 Aphrodite Sea mouse 3 Polynoe Scale worm 4 Eunice Palalo worm

10. Class : POLYCHAETA( Poly= Many; Chaetae= Setae) Sub Class : Sedentaria Sl. No Examples Common Names 1 Arenicola Lug worm 2 Sabella Peacock Worm 3 Chaetopterus Paddle worm 4 Aphritrite --

11. Class: OLIGOCHAETA( Oligo = Few; Chaeta= Setae) Lives in moist earth/ fresh water Cephalisation is not seen Tentacles, Palps , Cirri and Parapodia are absent Setae helps in locomotion Clitellum is present Prostomium is present but without eyes Metanephridia - excretory organs Hermaphrodites Circulatory system includes One or more hearts Feeds on decomposing material, acts as scavengers Development is direct Good power of regeneration

12. Class: OLIGOCHAETA( Oligo = Few; Chaeta= Setae) Divided into two orders they are Terricola : All terrestrial O ligochaetae annelids included Lymicola : All aquatic Oligochaetae annelids included Examples Megascolex Pheretima Lumbricus Tubifex Octochaetus Aelosoma

13. Class : HIRUDINEA/ DISCOPHORA Leeches Body with fixed segments subdivided to small segments called Annuli Dorso ventrally flattened body with anterior and posterior Suckers Parapodia and Setae are absent No cephalisation Five pairs of simple eyes at anterior end Coelom is highly reduced by Botroidal tissue Alimentary canal with crop divided into number of secae which are in pairs

14. Class : HIRUDINEA/ DISCOPHORA Some leeches have proboscis; others with jaws to wound the host body Open type circulatory system called haemocoelic system Hermaphrodites; clitellum during breeding only; testis are many and only one pair of ovaries Fertilisation is internal; development takes place in inside the cocoon and without larval forms Fresh watered/ marine leeches like Pantobdella Mostly parasitic; feed on dead and decaying; sangvivores

15. Class : HIRUDINEA/ DISCOPHORA Divided into four orders Acanthobdellida - Primitive individuals with short proboscis and setae Eg : Acanthobdella Rhyncobdellida -marine/fresh watered leeches with probosis Eg : Pantobdella , Glossiphonia Gnathobdellida - lives on land or in fresh water Eg : Hirudinaria , Heamodipsa Pharyngobdellida - pharynx not protrusible ; no jaws/ teeth Eg : Dina, Trocheta