Phylum Annelida
Name of phylum Annelida was first coined by Lamarck (1801) for the higher segmented
worms (Gr., annulus - little ring + eidos - form). Annelids are elongated, bilaterally symmetrical
and highly organized animals, in which the organs have grouped into definite systems.
Appearance of metamerism represents their greatest advancement, so that they are called
segmented worms in order to distinguish them from flatworms (Platyhelminthes) and
roundworms (Nematodes) which are not segmented. Their paired appendages, when present, are
never jointed. Their coelom, nephridia and cephalization are better developed than those of the
un-segmented worms.
They are the first animals to have a closed vascular system. Nervous system is
fundamentally similar to that of Arthropoda and embryology is not much different from that of
Mollusca.
General Characters of Annelida: -
- Mostly aquatic, some terrestrial.
- Burrowing or tubicolous.
- Some commensal and parasitic.
- Body elongated, bilaterally symmetrical, triploblastic, truly coelomate and meteorically segmented into similar metamers.
- Epidermis of a single layer of columnar epithelial cells, covered externally by a thin cuticle.
- Body wall dermo muscular.
- Outer muscle fibers circular, longitudinal.
- Locomotory organs are segmentally repeated chitinous bristles, called setae or chaetae, embedded in skin. May be 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 is closed.
- Respiratory pigments either hemoglobin or erythrocruorin dissolved in blood plasma.
- Respiration by moist skin or gills of parapodia and head.
- Excretory system consisting of metamerically disposed coiled tubes, called nephridia.
- Nervous system with a pair of cerebral ganglia (brain) and a double ventral nerve cord bearing ganglia and lateral nerves in each segment.
- Sensory organs include tactile organs, taste buds, statocysts, photoreceptor cells and sometimes eyes with lenses in some.
- Hermaphroditic or sexes separate, cleavage pattern spiral and determinate.
- Larva, when present, is a trochophore.
- Regeneration is common.
Classification of Annelida: -
Modern classification of phylum Annelida was proposed by Fauchold (1977) and Parker (1980). About 8,700 known species of annelid are divided into four main classes, primarily on the basis of the presence or absence of parapodia, setae, metamers, and other morphological features.
A. Class – Polychaeta (Gr., poly- many + chaite- hair)
- Chiefly marine, some in fresh water.
- Segmentation internal and external.
- Head distinct with eyes, palps and tentacles.
- Setae numerous, on lateral parapodia.
- Clitellum absent.
- Sexes separate.
- Gonads temporary and in many segments.
- Trochophore larva present.
1. Subclass – Erranitia
- Free-swimming, crawling, burrowing or tube-dwelling and predatory polychaetes.
- Segments numerous and similar, except for head and anal region.
- Prostomium distinct with sensory structures
- Parapodia with acicula and compound setae.
- Pharynx protrusible, enlarged and usually with jaws and teeth.
- Examples: Aphrodite (sea mouse), Polynoe, Phyllodoce, Tomopteris, Syllis, Nereis, Gycera, Eunice, Diopatra, Histriobdella.
2. Subclass - Sedentaria
- Sedentary polychaetes living in burrows or tubes.
- Body made of two or more regions, with dissimilar segments and parapodia.
- Prostomium small.
- No acicula and compound setae.
- Pharynx without jaws and teeth.
2. Class - Oligochaeta (Gr., oligos- few + chaite- hair)
- Mostly terrestrial, some in fresh water.
- Segmentation internal and external.
- 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 cocoon); development direct, no larval stages.
1. Order - Plesiopora plesiothecata
- Mostly aquatic.
- Male gonopores on segment immediately following that which contains testes.
- Spermathecae in the testes-containing segments, or nearby.
Examples: Aelosoma, Nais, Dero, Chaetogaster, Tubifex.
2. Order - Plesiopora prosothecata
- Spermathecae far anteriorly to the segment containing testes. Examples: Enchvtraeus.
3. Order - Prosopora
- Mostly aquatic.
- Male gonopores on the same segment containing testes, or on segment containing the second pair of testes. Example: Branchiobdella (parasitic).
4. Order - Opisthopora
- Mostly terrestrial earthworms.
- Male gonopores some distance behind the testes-containing segments.
- Examples: Lumbricus, Eisenia, Pheretima, Megascolex, Allolobophora, Dendrobaena
3. Class – Hirudinea (L., hirudo- leech)
- Freshwater, marine or terrestrial.
- Generally, ectoparasite, blood-sucking and carnivorous.
- Body with fixed number of segments (33).
- Each segment subdivided externally into annuli.
- Segmentation external without internal septa.
- Parapodia and setae absent.
- Both anterior and posterior ends of body with suckers.
- Coelom much reduced due to its filling by botryoidal tissue, and forms haemocoelomic sinuses.
- Hermaphroditic with one male and one female gonopore.
- Fertilization internal.
- Development in cocoons, direct without larval stages.
1. Order - Acanthobdellida
- Primitive without anterior suckers, proboscis and jaws.
- Setae present in 5 anterior segments.
- Coelom with compartments.
- Example: A single Russian genus and species (Acanthobdella) parasitic on salmon.
2. Order - Rhynchobdellida
- Only aquatic leeches, ectoparasitic.
- A protrusible proboscis with no jaws.
- Coelom without compartments.
- Bloodvasculare system separated from coelomic sinuses.
- Blood colourless.
3. Order - Gnathobdellida
- Aquatic or terrestrial.
- Ectoparasitic blood-sucking leeches.
- Pharynx non-eversible with 3 pairs of jaws.
- Examples: Hirudo, Hirudinaria, Haemadipsa.
4. Order - Pharyngobdellida
- Terrestrial and aquatic.
- Some predaceous.
- Pharynx non-protrusible.
- No teeth but one or two style may be present.
- Examples: Erpobdella, Dina.
4. Class - Archiannellida (Gr., arch- First)
- About one dozen genera of small, marine worms of unknown affinities.
- Segmentation chiefly internal.
- No parapodia and setae.
- Sexes usually separate.
- Usually, trochophore larva.
- Example: Polygordius, Dinophilus, protodrilus.
Hirudinaria granulose
Systematic Position: -
PHYLUM => ANNELIDA
CLASS => HIRUDINEA
ORDER => GNATHOBDELLIDA
FAMILY => HEIRUDINAE
GENUS => HIRUDINARIA
Species => granulos
Ecology: -
- Hirudinaria granulose, the Indian cattle leech, is found in India, Burma, Sri Lanka, Pakistan and Bangladesh.
- It occurs in fresh-water ponds, lakes, tanks, swamps and slow streams, where it either swim by vertical undulations or grips objects with its suckers and moves by looping.
- Like most ectoparasitic leeches, it has a blood-sucking (sanguivorous) habit, feeding on the blood of fish and frogs and also of cattle and men, who happen to enter the water inhabited by it.
- Though hermaphroditic, leeches copulate to bring about cross-fertilization.
- Eggs are deposited in cocoons.
- Body is elongated, Dorso-ventral-flattened and vermiform with flat ventral and convex dorsal surfaces.
- Development is direct, i.e., there are no free larval stages in the life-history.
Metamerism in Hirundinaria: -
In annelids the body consists of segments arranged in a linear repetitive fashion. This linear repetition of body segment is called metamerism. Each section or part of the body is called segment, somite or metamer.
Metamerism segmentation is first seen in animal kingdom in the body of annelids. In metameric
segmentation, body is divided into numerous body segments externally by groove and internally by septa. All the segments or metameres are same age and have all body organs such as musculature, blood vessels, nerves, ganglia, excretory organs and gonads etc. In earthworm and Nereis even the coelom is divided into segmental compartments by inter segmental septa.
But in annelids, the metamerism is limited to the trunk region of the body. The head with brain and
sense organs is represented by prostomium and the terminal portion at the posterior end with
anus is represented by pygidium.This two portions i.e., prostomium and pygidium are not true
metameres. In annelids metameism is described as bring complete because all segments or
metameres have segmented blood vessels, nerve, nephridia and coelom. Such segment also
called homonomous.
Significance of Metamerism: -
- Metamerism helps in locomotion in various ways. Annelids are able to locomotion like swimming and creeping by the help of the contraction of body wall muscles of body segments and coelomic fluid.
- Coelomic fluid in coelomic chamber acts as an hydraulic skeleton during burrowing and swimming.
- In higher classes like Arthropods and Chordates, each metamere of body is specialized for different functions. Hence, higher and complex animals evolved due to metamerism.
Parasitic Adaptations in Hirundinaria:-
Most leeches lead a semi-parasitic life, sucking blood of vertebrates. Correspondingly, they show several parasitic adaptations in their habits, habitat and structure.
✔Habitat: -
It inhabits freshwater ponds and pools visited frequently by men and cattle. Moreover, it prefers to live in shallow waters where it can easily hide under weeds, logs and stones.
✔Habits: -
Its active swimming habit is ideal for searching the host and escaping from predators.
✔Shape: -
Body is long, flattened and devoid of appendages, like parapodia, and hence suitable for aquatic life.
✔Slime gland: -
These are present in body wall. Their secretion keeps the body moist and slippery to prevent desiccation and reduces friction during locomotion.
✔Suckers: -
These serve as organs of locomotion and also provide firm adhesion to the host’s body at the time of feeding.
✔Jaws: -
The three jaws are specialized weapons for inflicting a painless triradiate wound on the host’s skin for sucking blood.
✔Suctorial pharynx: -
Mouth leads into a muscular pharynx connected with body wall by radiating muscles. Cavity of pharynx alternately expands and contracts to serve as a suction pump so that blood, oozing from the host’s would, is sucked in.
✔Hirudin: -
Slivery glands of leeches secrete an anticoagulating substance, called hirudin or anticoagulin, It prevents clotting of blood while the leech is taking its meal, thus ensuring a continuous supply of blood (vampire bats and hook worms also secretes a similar
substance to facilitate their feeding).
✔Spacious crop: -
Chances of getting a host are remote, so that supply of nutrient is very irregular and a matter of chance. Digestive tract is accordingly modified. At the time of single meal a leech obtains many times its own weight of blood, which is sufficient for several months or even a year. To accommodate this blood, the crop is spacious thin-walled elastic and capable of great dilatation. It is also produced into lateral pouches or storing pockets. It can, therefore, hold enough blood to last for months. However, some species that parasitize aquatic vertebrates remain attached to their hosts.
✔Slow digestion: -
After a meal, leech drops off, remains torpid and digests blood at a very slow pace. Last chamber of crop opens behind into stomach through a sphinctered aperture, so that blood passes from crop into stomach with extreme slowness. Digestion of a “crop full of blood” takes many months and thus a single meal lasts for several months. For this reason also leeches lack elaborate digestive juices and enzymes.
✔Sense organs: -
These are well-developed and provide the animal with greater opportunities of life.
✔Hermaphroditism: -
This doubles the rate of reproduction as, after copulation, both individuals lay eggs.
✔Development: -
It takes place within the cocoon which serves as a protective covering. Further, development is quick, and completed within a fortnight to ensure the maintenance of a regular population.
Multiple choice questions:-
1. In leech locomotion occurs by: -
(a) Setae [ ] (b) Parapodia [ ] (c) Undulating movements [√] (d) All of these [ ]
2. The saliva of leech contains an anticoagulant called: -
(a) Histidine [ ] (b) Hirudin [√] (c) Heparin [ ] (d) Histamine [ ]
3. Coelom filled with connective tissue and botryoidal tissue has come across in
(a) Earthworm [ ] (b) Nereis [ ] (c) Leech [√ ] (d) Ascaris [ ]
4. Which one of the following is an ectoparasite annelid
(a) Hirudinaria [√] (b) Lumbricus [ ] (c) Pheretima [ ] (d) Ascaris [ ]
5. Botryoidal tissue is found in
(a) Unio [ ] (b) Ascaris [ (c) Hirudinaria [√] (d) Nereis [ ]
6. How many numbers of somites are present in the body of leech?
(a) 20 [ ] (b) 40[ ] (c) 50 [ ] (d) 33 [√]
7. In leech the excretion is: -
(a) Uricotelic [ ] (b) Ammonotelic [√] (c) Ureotelic [ ] (d) None of these [ ]
8. Leech is
(a) Carnivorous [ ] (b) Omnivorous [ ] (c) Sanguivorous [√] (d) Herbivorous [ ]
9. Saliva of leeches contain an anticoagulant called
(a) Haemoglobin [ ] (b) Hirudin [√] (c) Heparin [ ] (d) Histamine. [ ]
10. Common cattle leech belongs to the genus
(a) Megascolex [ ] (b) Neanthes [ ] (c) Arenicola [ ] (d) Hirudinaria [√]
11. The saliva of leech has an anticoagulant called
(a) Heparin [ ] (b) Hirudin [√] (c) Chloragosomes [ ] (d) None of these [ ]
12. How many chambers are found in the crop of leech?
(a) Six [ ] (b) Eight [ ] (c) Nine [ ] (d) Ten [√]
13. Leech is a blood sucking animal, nutritionally, therefore leech is
(a) Herbivorous [ ] (b) Carnivorous [ ] (c) Sangivorous [√ ] (d) Omnivorous [ ]
14. In which segment do you find the ovisac in leech?
(a) 8th [ ] (b) 11th[√] (c) 15th[ ] (d) 13th[ ].
15. Which segment possesses nephridia in Hirudinaria?
(a) 7-10th segment [ ] (b) 6-22 segments [√] (c) 10-20 segments [ ] (d) 7-18 segments [ ]
16. Female genital opening of Hirudinaria is present in
(a) Ist annule of 10th segment [ ] (b) Ist annule of 11th segment [ ] (c) 2nd annule of 10th
(d) 2nd annule of 11th segment [√]
17. The posterior sucker of Hirudinaria is formed by the union of
(a) 1 segment [ ] (b) 7 segments [√] (c) 25 segments [ ] (d) 33 segments [ ]
18. The number of segments in Hirudinaria is
(a) 109 [ ] (b) 33[√] (c) 26 [ ] (d) Numerous [ ]
20. In Hirudinaria space between body wall and canal is filled with the
(a) Botryoidal [√] (b) Connective tissue [ ] (c) Hoemocoelomic fluid [ ] (d) None [ ].
21. Hirudinaria is
(a) Herbivorous [ ] (b) Carnivorous [ ] (c) Omnivorous [ ] (d) Sanguivorous [√]
22. A temporary clitellum is formed in Hirudinaria’s segments
(a) 7th,8th and 9th[ ] (b) 9th to 11th[√] (c) 11th to 13th[ ] (d) None [ ]
23. Number of annular receptor in each annulus
(a) 18[ ] (b) 18 on dorsal and 18 on ventral [√] (c) 9 [ ] (d) None of the above. [ ]
24. Hirudinaria contains
(a) Slime gland [ ] (b) Sucker gland [ ] (c) Clitellar gland [ ] (d) All the above [√]
25. Velum is present in
(a) Pheretima [ ] (b) Hirudinaria [√] (c) Ascaris [ ] (d) All the above. [ ]
26.In Hirudinaria there is no special organ for
(a) Digestion [ ] (b) Excretion [ ] (c) Respiration [√] (d) Reproduction. [ ]
27. Number of testes in Hirudinaria is:
(a) 10 pairs [ ] (b) 11 pairs [√] (c) 12 pairs [ ] (d) 13 pairs [ ].
28. How is phylum Anellida advanced over Nemathelminthes?
(a)Metameric segmentation [ ] (b) True coelom [ ] (c) Closed circulation [ ] (d) All of the
above [√]
29. The animal bearing numerous setae are kept in class
(a) Hirudinea [ ] (b) Oligochaeta [ ] (c) Polychaeta [√] (d) Onychophora [ ]
30. In which class of phylum Annelida one pair of ovaries and many pairs of testes are found?
(a) Polychaeta [ ] (b) Oligochaeta [ ] (c) Hirudinea (d) Archiannelida [ ]
31. Which one of these is the primary characteristic of phylum Annelida?
(a) Trochophore larva in life cycle [ ] (b) Metameric segmentation [√] (c) Excretion by flame
cells [ ] (d) Body covered by ciliated epidermis. [ ]
32. Aphrodite is commonly known as
(a) Lung worm [ ] (b) Paddle worm [ ] (c) Sand worm [ ] (d) Sea mouse [√]
33. Larval form of Polychaeta is known as
(a) Tornaria [ ] (b) Glochidium [ ] (c) Trochophore [√] (d) Bipinnaria [ ].
34. Smooth blood worm is
(a) Aphrodite [ ] (b) Glycera [ ] (c) Hirudinaria [√] (d) Terebella [ ]
35. In Lumbricus, clitellum is present in segments
(a) 33 to 37 [√] (b) 22 to 27 [ ] (c) 54 to 60 [ ] (d) 46 to 56 [ ]
36. A triploblastic, bilaterally symmetrical, elongated and vermiform body is characteristic of
(a) Coelenterates [ ] (b) Arthropods [ ] (c) Annelids [√] (d) None of the above [ ]
37. Tube dwelling polychaetes are known as
(a) Burrowing [√] (b) Planktonic [ ] (c) Pelagic [ ] (d) Tubicolous [ ]
38. In Polychaeta, the nature of seta is
(a) Numerous [√] (b) Occur singly [ ] (c) Occur in bundles [ ] (d) Fused [ ]
39. Presence of coelom and metamerism are the most important characters in
(a) Helminths [ ] (b) Arhhropods [ ] (c) Annelids [√] (d) Coelenterates [ ]
40. The origin of the nephridium is
(a) Germinal [ ] (b) Ectodermal [ ] (c) Mesodermal [√] (d) Endodermal [ ]
41. Cuticle of annelids is
(a)Non-chitinous and albuminoid (b) Chitinous [√] (c) Chitinous albuminoid [ ] (d) Non
chitinous [ ]
42. The body cavity of Hirudo is filled with
(a) Connective tissue [ ] (b) Parenchyma tissue [ ] (c) Botryoidal tissue [ ] (d) Coelomic fluid [√]
43. Tube within a tube body plan is found in
(a) Pheretima posthuma [ ] (b) Hydra [ ] (c) Rana tigrina [√] (d) Lepus cuniculus [ ]
44. Arenicola is commonly known as
(a) Lugworm[√] (b) Paddle worm[ ] (c) Sea pen [ ] (d) Potato worm. [ ]
45. Nereis is commonly known as
(a) Clam worm [√] (b) Earthworm [ ] (c) Skate sucker [ ] (d) Sea fan. [ ]
46. Sucking of human blood by the leech is called
(a) Blood sucking [√] (b) Phlebotomy [ ] (c) Autotomy [ ] (d) Phrynotomy [ ]
47. The coelom in Annelida is
(a) Pseudocoelic [ ] (b) Enterocoelic [ ] (c) Schizocoelic [√] (d) Acoelous [ ]
48. Lug worm is scientifically known as
(a) Nereis [ ] (b) Arenicola [√] (c) Aphrodite [ ] (d) Polynoe [ ]
49. Sabella is generally known as
(a) Rag worm [ ] (b) Scale worm [ ] (c) Peacock worm [√] (d) None [ ]
50. Which is known as blood worm?
(a) Terebella [ ] (b) Tubifex [ ] (c) Lumbricus [√] (d) Nereis [ ].
51. The ‘Tubifex’ is
(a) Blood parasite [ ] (b) Sand dweller [√] (c) Fresh water [ ] (d) Parasite [ ].
52. Medicinal leech is
(a) Hirudinaria [ ] (b) Hirudinaria japanica [ ] (c) Hirudo medicinalis [√]
(d) Hirudinaria viridis [ ]
53. Sipunculus is commonly known as
(a) Nut worm [ ] (b) Pea nut worm [√] (c) Peacock worm [ ] (d) None [ ]
54. The annelid larva is
(a) Bipinnaria [ ] (b) Trochophore [ ] (c) Cercaria [√] (d) None [ ]
Terminal Question :-
1. Write important adaptive features of Hirudinaria?
2. Describe the features indicating the adaptations of leech to lead an ectoparasitic life?
3. Which organs does the female reproductive system of leech comprise? Write the location of
ovaries?
4. Write, in brief, about the mode of locomotion of leech?
5. Write a short note on haemocoelomic system of leech?
6. In how many classes is phylum Annelida divided?
7. Give the name of larvae of Annelida?
8. Name the kind of segmentation found in annelids?
9. What is the feeding habit of Hirudinaria?
10. How many testes are present in Hirudinaria?
No comments:
Post a Comment