The word Annelida is derived from the Latin word annelus meaning small ring and eidos meaning shape. Animal bodies that are triploblastic, cylindrical, ring-like segments or metameres are called Annelida. The animals of this phase are known as ringworms or segmented worms. Phlebotomy is the process in which a starved leech is attached to the body to suck the contaminated blood from the body. The number of species in this category is about 17,338. Lamark (1809) identified soft-bodied animals as Annelida.
Characteristics of Annelida
1. Body long, cylindrical, bilaterally symmetrical and with true cylomes.
2. The body is segmented and composed of many segments or metameres similar to rings.
3. Movement organs are chitinous seatae or parapodia.
4. Patchy excretory organs called nephridia are located in almost every segment. It is called segmental organ.
5. The body contains the clitellum and secretes mucus.
6. The alimentary canal is cylindrical and complete and consists of oral and anal openings.
7. Blood is red. Plasma contains hemoglobin, heme-erythrin or chloroquine.
8. The body is composed of chitinless and soft cuticle.
9. The larval stage of the life cycle consists of trochophores.
10. They are unisexual or bisexual. Reproduction occurs sexually and asexually.
Classification of Annelida
The order Annelida is divided into 3 classes.
1. Polychaeta: Their body parts are covered with hairs. locomotion parapodia. Sensory organ is nucell organ. They are mostly marine. For example, Nereis caudata.
2. Oligochaeta: These are leech-like creatures. They live by digging holes. For example, Metaphire posthuma.
3. Hirudinia: They have clitellum. There is a substance called hirudin in the body. For example, Hirudinaria medicinalis.
Some animals of Annelida
Leech- Hirudinaria medicinalis
Nereis- Nereis/Neanthes caudata
Spectacular insect – Amphrite figulus
Arenicola – Arenicola marina
Earthworm- Metaphire posthuma
Terebella lapidaria
Haemopis- Haemopis terrestris
Pontopdella- Pontopdella muricata
Hairy Worm- Hediste diversicolor
Blood worm- Glycera convoluta
Lumbricus- Lumbricus terrestris
Parchment worm- Chaetopterus variopedatus
Red worm – Eisenia foetida
Tubifex – Tubifex tubifex
Sea Lice – Aphrodite aculeata
Ornate Worm- Aphrodite ornata
Fan worm- Serpula vermicularis
Nephridia
Nephridia is a type of excretory organ. nephridia It collects nitrogenous wastes. Passes waste material to the intestines. Plays a role in osmoregulation.