biology project

what are annelids ?

annelids are a segmented worm of the phylum Annelida, such as an earthworm or leech.


  • The polychaetes are the largest and most primitive class of annelids, with more than 5300 described species, most of them marine.
  • Although the majority are from 5 to 10 cm long, some are less than a millimeter, and others may be as long as 3 meters.
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  • When oligochaetes mate, their anterior ends face in opposite directions. Their ventral surfaces touch. Sperm cells are released by both oligochaetes and held to each organism's body by a mucus cocoon. Egg cells are released into the mucus and fertilization occurs. The oligochaete sheds the mucous 'package' and new oligochaetes form.
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  • the mouth can be bigger than the rest of the body

  • A digestive channel runs in full body length to the posterior end

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  • The fundamental characteristic of the phylum is the division of the body into a linear series of cylindrical segments, or metameres

  • they can be either herbivorous or carnivores

  • some physical are chaetae ( hairs made of chitin), segmentation, 3 cell layers, true coelom, head develops first ( protostomal)

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Annelids Biology Movie