PHYLUM ANNELIDA

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1) PHYLUM ANNELIDA

1.1) HISTORY

1.2) DIAGNOSTIC CHARACTERS OF PHYLUM ANNELIDA

1.3) CLASSIFICATION OF PHYLUM ANNELIDA

1.3.1) CLASS I POLYCHAETA

1.3.2) CLASS II OLIGOCHAETA

1.3.3) CLASS III HIRUDINEA

HISTORY

Phylum Annelida are truly coelomate animals with metameric segmentation. Capacious coelom and its divisions by septa into separate water tight compartments gives much greater control in the use of the hydrostatic skeleton so that changes in shape, shortening, lengthening or bending can be achieved in one segment without unduly influencing the adjacent segments. Phylum annelida includes primitive Archiannelids, Polychaetes and Oligochaetes. Primitive annelids are marine forms which might have given rise to polychaetes and oligochaetes separately. Polychaetes are polyphylectic. Polychaetes represent one line of evolution while Oligochaetes and their related forms second line of evolution. Echiuroids, sipunculids, priapulids and myzostomaria listed as classes of annelids are considered as independent phyla. However the fundamental pattern evolved in Annelids (coelom and segmentation) continue up to man.

DIAGNOSTIC CHARACTERS OF PHYLUM ANNELIDA

Segmented and coelomate animals.
Segmentation metameric.
Closed circulation.
Excretory organs metanephridia.
Exoskeleton absent.
Fresh-water, marine, terrestrial, burrowing or tubicolours.

CLASSIFICATION OF PHYLUM ANNELIDA

CLASS I POLYCHAETA

Many setae or hair in each segment.
Clitellum absent.
Larva trochophore.

Order 1 Errantia

1. Free moving or swimmillg.
2. Locomotary organs parapodia.
  Example :- Nereis, Heteronereis, Aphrodite, Polynoe, Eunice, Syllis, Glycera, Tomopteris.

Order 2 Tubicola

1. Tubicolous animals.
2. Segments greatly modified.
  Example :- Chaetopterus, Sabella, Parasabella

Order 3 Sedentaria

1. Sedentary animals.
2. Body divided into different regions.
  Example :- Arenicola, Amphitrite, Terebella, Serpuia, spirorbis, Sternaspis.

CLASS II OLIGOCHAETA

Few setae in each segment.
Citellum present.

Order 1 Archioligochaeta

1. Primitive forms.
2. Small and fresh-water.
  Example :- Aelosoma, Tubifex, Nais, Dero

Order 2 Neooligochaeta

1. Modem earthworms.
2. Terrestrial and burrowing.
  Example :- Pheretima, Etyphoeus, Lumbricus.

CLASS III HIRUDINEA

It includes leeches.
Anterior and posterior suckers present. Parapodia absent.
Only external segmentation.

Order 1 Acanthobdellida

1. Primitive leeches.
2. Coelom with compartments.
3. Anterior sucker absent.
  Example :- Acanthobdella.

Order 2 Rhynchobdellida or Agnathobdellida

- Ectoparasitic aquatic leeches.
- Anterior sucker absent.
  Example :- Pontobdella, Glossiphonia, Branchillion.

Order 3 Arhynchobdellida or Gnathobellida

1. Ectoparasitic blood sucking leeches.
2. Both anterior and posterior suckers present.
  Example :- Hirudo medicinalis, Haemopis, Nephelis,
  Hirudinaria.