Character classification and economic impotantant of Annelida.

The general character of Annelida.

• Mostly aquatic some terrestrial. Burrowing or tubicolous.Some commensal and parasitic.
• Body elongated, bilaterally symmetrical, triploblastic, truely coelomate and metamerically segmented into similar metamers.
• Epidermis of a single layer of columnar epithelial cells covered externally by a thin cuticle not made of chitin.
• Body wall dermo- muscular. Outer muscle fibres circular, inner longitudinal.
• Locomotory organs are segmentally repeated chitinous bristles, called setae or chaetae, embedded in the skin.Maybe borne by lateral fleshy appendages or parapodia.
• Coelom, true, schizocoelous. Mostly well - developed except in leeches. Usually divided into compartments by transverse septa. Coelomic fluid with cells or corpuscles.
• Digestive system straight and complete. Digestion entirely extracellular.
• Blood vascular system closed. Respiratory pigments either haemoglobin or erythrocruorin dissolve in blood plasma.
• Respiration by moist skin or gills of parapodia and head.
• An excretory system consisting of metamerically disposed of coiled tubes called nephridia.
• Nervous system with a pair of cerebral ganglia and a double ventral in each segment.
• Sensory organs include tactile organ, tastebuds, statocysts, photoreceptor cells and sometimes eyes lenses in some.
• Hermaphroditic or sexes are separate cleavage spiral and determinate. Regeneration common.

Classification of Annelida.

Annelida is divided into four main classes, primarily on the basis of the presence or absence of parapodia.setae, metameres, and the morphological feature.About 8,700 known species of Annelida are divided into four main classes, The character of class with examples is discussed below.

Class 1.Polychaeta

(Gr., polys, many+chaite, hair )

• Chiefly marine, some in freshwater.
• Segmentation internal and external.
• Head distinct with eyes, palps and tentacles.
• Setae numerous, on lateral parapodia.
• Clitellum absent.
• Sexes separated. Gonads temporary and in many segments.
• Trochophore larva present.

Attempts to arrange families into order has not proved satisfactory.It is unusual, therefore, to divide polychaetes into two subclasses. Errantia and Sedentaria, after Fauvel (1959). However, according to Dab (1963), this sub- division is artificial and not a nature one.

Sub -class 1.Errantia.

• Free swimming, crawling, burrowing or tube -dwelling and predatory polychaetes.
• Segment numerous and similar, except for head and anal region.
• Prostomium distinct with sensory structures.
• Parapodia with acicular and composed setae.
• Pharynx protrusible, enlarged and usually jaws and teeth.

Example : Aphrodite, poly now, Glycera.

Sub- class 2. Sedentary.

• Sedentary polychaetes living in burrows or tubes.
• Body made of two or more regions, with dissimilar segment and parapodia.
• Prostomium small.
• No acicula and compound setae.
• Pharynx without jaws and teeth.

Example: Chaetopterus, Arenicola, Owenia, Sabella, Sabellaria, Terebella, Amphritrite, Pomatoceros, Spirorbis, Serpula.

Class 2. Oligochaeta

(Gr., oligos, few + chair, hair)

• Mostly terrestrial, some in fresh water.
• Segmentation external and enternal.
• Head distinct, without sensory organs.
• Setae few, embedded in skin. Parapodia absent.
• Glandular clitellum present for cocoon formation.
• Hermaphroditic.Testes anterior to ovaries.
• Fertilization external ( in coccon) : development direct, no larval stages.

Order 1. Plesiopora plesiothecata

• Mostly aquatic.
• Male gonophores on segment immediately following that which contain testes.
• Spermathecae in the testes -containing segments, or nearby.

Example: Aelosoma, Nais,Dero, Chaetgaster, Tubifex.

Order 2 Plesiopora Prosothecata

Spermathecae far anteriorly to the segment containing testes.

Example: Enchytraeus.

Order 3. Prosopora

• Mostly aquatic.
• Male gonopore on the same segment containing testes, or on segment containing the second pair of testes.

Example : Branchiobdella (Parasitic)

Order 4.Opisthopora

• Mostly terrestrials earthworm
• Male gonopore some distance behind the testes- containing segments

Example : Lumbricus, Eisenia, Pheretima, Megascolex, Allolobophora,Dendobaena.

Class 3. Hirudinea.

Gr,.Lhirudo, leech)

• Fresh -water, marine or terrestrial. Generally ectoparasitic , blood -sucking or carnivorous.
• Body wall fixed number of segment (33) Each segment subdivided externally into annuli
• Segmentation external without internal septa, Parapodia and setae absent.
• Both anterior and posterior ends of a body with suckers.
• Coelom much reduced due to its filling by botryoidal tissue and forms haemo coelomic sinuses.
• Hermaphroditic w ith one male and one female gonopore. Fertilization internal Development in cocoons directs without larval stages.

Order 1. Acanthobdellida:

• Primitive, without anterior sucker, proboscis,and jaws.
• Setae present in 5 anterior segments.
• Coelom with compartments.

Example Acanthobdella:

Order 2. Rhynchobdellidellida

• Only aquatic leeches, ectoparasitic.
• A protrusible proboscis with no jaws.
• Coelom without compartments.
• Blood vascular system separated from coelomic sinuses.Blood colourless.

Example : Glossiphonia, Placobdella, Branchellion, Ozorbranchus.

Order 4. Ganthobdellida

• Aquatic or terrestrial. Ectoparasitic blood sucking leeches.
• Pharynx non-reversible with 3 pairs of jaws.

Example : Hirudo, Hirudinaria,Haemadipsa.

Order 4. Pharyngobdellida

• Terrestrial and aquatic. some predaceous.
• Pharynx on- protrusible. No teeth but one or two styles may be present.

Example Erpobdella, Dina.

Class 4. Archinnalida:

(Gr., arch,first)

• About one dozen genera of small, marine, worms of unknown affinities.
• Segmented chiefly internal. No parapodia and setae.
• Sexes usually separate.
• Usually trochophore larva.

Example : Polygordius, Dinophilus, Protodriluse.

Economics importance of Annelida.

Annelida is of considerable economic importance to man.They are directly useful or harmful and are associated with the man in many ways.

A.Useful Annelids.

1.As bait and food

All over the world they are used as bait for fishing. Arenicola, Glycerin, earthworms, leeches etc are used as bait for fishes. Various methods are employed to drive them out of their burrows for making large collections. Some of these include jarring soil by beating a stick driven into it, pouring poisonous chemical solution such as mercuric chloride on the ground and even used an electric current. They form the best food of fish in aquaria. A small white earthworm is often grown in soil and used to feed aquarium fish and small laboratory animal.Similarly, They are used in food in different ways of as below;

• The epitopes of Eunice (Palolo worms) are used as food by the native people.Epitopes are highly nutritive constituting of pure yolk- laden eggs. Palolo worm of pacific is Eunice, Viridis, that of Atlantic is Eunice schema cep ha, and of Japan is metencephala Iraqi.
• The earthworm forms the best food for aquaria fishes, eg, a small earthworm Enchytraeusalbidus is commonly used to feed aquarium fish and small laboratory animals.They are also used as food by uncivilized, human in many parts of the world.They are also taken as food by certain birds such as robins and chicken.They are also eaten by frogs, snakes lizards, centipedes and other predatory invertebrates.
• Leeches are used as food by many fishes, ducks, plovers, turtles and mammals.

2.Reef -building agents:Some sand and lime-secreting tuberculous polychaetes are an important reef-building agent in some parts of the world.

3.In medicine:They are mostly used in medicine to cured- from different diseases .Some of the important used of Annelida is for :

• Earthworm was used in medicines. They were used to prepare medicines to stones in the bladder, for jaundice , for piles, gout, rheumatism, sexual impotency, etc. Even now, they are used for making medicine by the Japanese , the Chinese and the Indians.
• In China, Japan nd India, leeches extract the blood in painless- manner has been long utilized in surgery. It was used for blood letting (Phlebotomy)i,e to discard bad blood to cure disease, reduce swelling and dislocation.In 1863, 7 million leeches used in London and Paris hospital alone. The Ayurvedic practice also used particularly or drugs to prevent greying of hair, of old age. They are used as metric medicine in fits, tonsilitis, baldness etc.
• Hirudin was extracted from leeches and used as an anticoagulant.

4..As Laboratory Animals:

Earthworm and leeches are easily obtained and are a convenient size for dissection.They are, therefore, universally employed for class studies and for investigations in general and comparative physiology.

5..Improvement of Agriculture:

Earthworm is in general beneficial to agriculture. Although, they may sometimes do damage to young and tender plants , yet they are good friends to the gardeners and farmer as they are continually ploughing and manuring the soil.

They improve the soil as they continually ploughing and manuring the soil. Their habit of burrowing and swallows earth increases fertility,of the soil in many ways. Burrows improve of soil aeration increase the depth of top soil by burrowing into sub- soil, bringing to the surface. Thus,the land becomes more porous and serves for better penetration of air and moisture.This facilitates the growth of root and thus agricultural yield, increased.

6..Tubifex (Blood- worm) helps in purification of polluted fresh- water bodies.

B. Harmful Annelids:

• In some cases, Leeches are generally harmful.They cause the nuisance to man and cattle both in water and on land by sucking blood.Leeches destroy insect larva, worms, molluscs, other invertebrates, and attack .
• In some cases, Earthworm is,harmful to man .They may damage young and tender plants.Their burrows may sometimes cause loss of water by seepage. Sometimes some species live as external parasites of frog and man.They may also bring disease germs from the carcases of buried animals and may infect other animals .They also serve as intermediate host of certain parasites such as tapeworm(e,g Amoebataenia Sphenoids) and tapeworm (e,g Syngamus ) of chicken and the lung nematode(e,g,) Metastronglyplus elongates).
• Some earthworm act as pests e.g, Pheretima elongate damage the roots of Piper Betel:
• Malaria paludicole causes injuries to roots of paddy plants
• Personing damages the stems of cardamom.

Reference:

Aggarwal Sarita. A Text Book of Biology. New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L., Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.biologydiscussion.com/

http://www.parasitesinhumans.org/

https://web.stanford.edu/class/

https://en.m.wikipedia.org/wiki/Hirudo_medicinalis