Phylum – Annelida
👉They may be aquatic (marine and fresh water) or
terrestrial; free-living, and sometimes parasitic.
👉They exhibit organ-system level of body
organisation and bilateral symmetry.
👉They are
triploblastic, metamerically segmented and
coelomate animals.
👉Their body surface is
distinctly marked out into segments or
metameres and, hence, the phylum name
Annelida (Latin, annulus : little ring)
👉They possess longitudinal and circular muscles
which help in locomotion.
👉Aquatic annelids like
Nereis possess lateral appendages, parapodia,
which help in swimming.
👉A closed circulatory
system is present.
👉Nephridia (sing. nephridium)
help in osmoregulation and excretion.
👉Neural
system consists of paired ganglia (sing. ganglion)
connected by lateral nerves to a double ventral
nerve cord.
👉Nereis, an aquatic form, is dioecious,
but earthworms and leeches are monoecious.
Reproduction is sexual.
👉Examples : Nereis, Pheretima (Earthworm) and
Hirudinaria (Blood sucking leech).
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