(L. Annelus – a little ring)
The term Annelida was coined by Lamarck.
VVI Examples of Phylum Annelida for Entrance Exams are:
- Nereis (Sandworm or Clam worm)
- Aphrodite (Sea mouse)
- Chaetopterus (Paddle worm)
- Arenicola (Lungworm)
- Pheretima (The common earthworm)
- Lumbricus (English or European earthworm)
- Tubifex (Blood earthworm)
- Megascolex
- Hirudinaria (Cattle leech)
- Hirudo (Medicinal leech)
- Pontobdella (Skate sucker)
- Polygordius (Living fossil)
Characteristics of Phylum Annelida
· Triploblastic, bilaterally symmetrical, first coelomate (Schizocoel derived from splitting of mesoderm), segmented animals with the organ-system level of body organization, tube within a tube body plan and complete digestive system.· Mostly aquatic, both fresh water and marine.
· Generally burrowing, some sedentary or free-living while others are ectoparasites.
· They are metamerically segmented i.e. external segmentation (grooves) corresponds with internal segmentation (septa).
· Locomotary organs are paired setae or chaetae or in each segment which is accompanied by the musculature of skin.
· Digestive system is well-developed which consists of a straight alimentary canal and digestion is entirely extracellular.
· Respiration takes place through moist general body surface by diffusion.
· Excretion occurs by nephridia present on each segment.
· Circulatory system is closed type appears first time in the animal kingdom or first heart bearer.
Blood is red in colour due to haemoglobin.
(iii) Hirudinea
· They are ectoparasites or sanguivorous with an anterior and posterior sucker.
· Locomotary organs are suckers.
· Hirudin (an anticoagulant) is present in saliva.
· Distinct head absent but the presence of suckers.
· Clitellum absent or temporarily developed in 9th-11th segments during the breeding season.
· Presence of Botryoidal tissue.
· Hermaphrodite
· Fertilization: external in the cocoon.
· Development: direct.
· Body consists of a definite number of segments (i.e. 33).
Examples: Hirudinaria (Cattle leech)
Hirudo (Medicinal leech)
Pontobdella (Skate sucker)
(iv) Archiannelida
· Exclusively marine forms.
· No external segmentation but internal segmentation is complete.
· Distinct head is absent.
· Clitellum is absent.
· No parapodia and no setae.
· Sexes are usually separate and they rarely unite.
· Trochophore larva is present.
Examples: Polygordius (Living fossil)
Haemoglobin is dissolved in plasm.
· Presence of Neurogenic heart. Some polychactes contain chlorocruorin (green pigment).
· Body is covered by a transparent moist non-chitinous cuticle secreted by ectoderm.
· Nervous system is well-developed.
· The nervous system consists of a pair of dorsal cerebral ganglia, a pair of peri-pharyngeal connectives (nerve ring), and a double solid ventral nerve cord having a ganglion and lateral nerves in each segment.
· Hermaphrodite or exhibit sexual dimorphism.
· Larva is Trochophore type e.g. Nereis, Pheretima posthuma, Hirudinaria, etc.
· Various species of polynoe (scale worm) and chaetopterus (paddle-worm) are luminous in dark.
· Respiratory pigments are chlorocrunin and hemocyanin.
(i) Polychaeta (Poly – many, chaite – hair)
(ii) Oligochaeta (Oligo–few, chaite–hair)
· Locomotary organs are setae found in each segment.
· Mostly terrestrial, some are freshwater.
· Body lacks a distinct head.
· Body is segmented externally as well as internally.
· Clitellum is present.
· Hermaphrodite, development is direct (absence of larval stage), fertilization is external by cocoon formation.
Examples: Pheretima (The common earthworm)
Lumbricus (English or European earthworm)
Tubifex (Blood earthworm)
Megascolex
· Presence of Neurogenic heart. Some polychactes contain chlorocruorin (green pigment).
· Body is covered by a transparent moist non-chitinous cuticle secreted by ectoderm.
· Nervous system is well-developed.
· The nervous system consists of a pair of dorsal cerebral ganglia, a pair of peri-pharyngeal connectives (nerve ring), and a double solid ventral nerve cord having a ganglion and lateral nerves in each segment.
· Hermaphrodite or exhibit sexual dimorphism.
· Larva is Trochophore type e.g. Nereis, Pheretima posthuma, Hirudinaria, etc.
· Various species of polynoe (scale worm) and chaetopterus (paddle-worm) are luminous in dark.
· Respiratory pigments are chlorocrunin and hemocyanin.
Classification of Phylum Annelida
On the basis of locomotory organs, they are divided into 4 classes.(i) Polychaeta (Poly – many, chaite – hair)
· They are marine and carnivorous.
· Body is elongated and segmented.
· Body bears a distinct head. The Head bears two pairs of eyes and tentacles.
· Clitellum is absent.
· Cirri or branches may be present for respiration.
· Sexes are separate, fertilization is external and development is indirect.
· Locomotary organs are parapodia.
· No clitellum and cocoon-formation and a free-swimming trochophore larval stage are present.
Examples: Nereis (Sandworm or Clam worm)
Aphrodite (Sea mouse)
Chaetopterus (Paddle worm)
Arenicola (Lungworm)
· Body is elongated and segmented.
· Body bears a distinct head. The Head bears two pairs of eyes and tentacles.
· Clitellum is absent.
· Cirri or branches may be present for respiration.
· Sexes are separate, fertilization is external and development is indirect.
· Locomotary organs are parapodia.
· No clitellum and cocoon-formation and a free-swimming trochophore larval stage are present.
Examples: Nereis (Sandworm or Clam worm)
Aphrodite (Sea mouse)
Chaetopterus (Paddle worm)
Arenicola (Lungworm)
· Locomotary organs are setae found in each segment.
· Mostly terrestrial, some are freshwater.
· Body lacks a distinct head.
· Body is segmented externally as well as internally.
· Clitellum is present.
· Hermaphrodite, development is direct (absence of larval stage), fertilization is external by cocoon formation.
Examples: Pheretima (The common earthworm)
Lumbricus (English or European earthworm)
Tubifex (Blood earthworm)
Megascolex
(iii) Hirudinea
· They are ectoparasites or sanguivorous with an anterior and posterior sucker.
· Locomotary organs are suckers.
· Hirudin (an anticoagulant) is present in saliva.
· Distinct head absent but the presence of suckers.
· Clitellum absent or temporarily developed in 9th-11th segments during the breeding season.
· Presence of Botryoidal tissue.
· Hermaphrodite
· Fertilization: external in the cocoon.
· Development: direct.
· Body consists of a definite number of segments (i.e. 33).
Examples: Hirudinaria (Cattle leech)
Hirudo (Medicinal leech)
Pontobdella (Skate sucker)
(iv) Archiannelida
· Exclusively marine forms.
· No external segmentation but internal segmentation is complete.
· Distinct head is absent.
· Clitellum is absent.
· No parapodia and no setae.
· Sexes are usually separate and they rarely unite.
· Trochophore larva is present.
Examples: Polygordius (Living fossil)
Also, Read our Other Notes Important for Entrance Exams:
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- Leishmania donovani
- Amoeba proteus
- Phylum Porifera
- Phylum Coelenterata
- Hydra
- Phylum Ctenophora
- Phylum Platyhelminthes
- Liver fluke
- Tapeworm
- Phylum Nemathelminthes
- Ascaris lumbricoides (Roundworm)
- Wucheria bancrofti (Filarial worm)
- Ancylostoma (Hookworm)
- Enterobius (Pinworm)
- Phylum Annelida
- Earthworm
- Phylum Arthropoda
- Cockroach
- Mosquito
- Phylum Mollusca
- Phylum Echinodermata
- Phylum Chordata