PHYLUMPHYLUM – –

ANNELIDAANNELIDA

● Organ system level of organisationOrgan system level of organisation● Bilateral symmetryBilateral symmetry● Triploblastic organisationTriploblastic organisation● CoelomatesCoelomates● Metamerically segmentedMetamerically segmented

Their body surface isTheir body surface is● distinctly marked out distinctly marked out

into segments or into segments or metameres (Latin, metameres (Latin, annulus : little ring) annulus : little ring) and, hence, the and, hence, the phylum name phylum name AnnelidaAnnelida

HABIT AND HABITATHABIT AND HABITATThey may be aquatic (marine and fresh water) or They may be aquatic (marine and fresh water) or terrestrial; free-living, and sometimes parasitic.terrestrial; free-living, and sometimes parasitic.

● Possess longitudinal and circular muscles Possess longitudinal and circular muscles which help in locomotion.which help in locomotion.

PARAPODIA

Aquatic animals like Neries possess lateral Aquatic animals like Neries possess lateral appendages, parapodia which help in appendages, parapodia which help in swimming. swimming.

AA closed circulatory system is closed circulatory system is present.present.

Nephridia (sing. Nephridium) – help in Nephridia (sing. Nephridium) – help in osmoregulation and excretionosmoregulation and excretion

Neural system consists of paired ganglia Neural system consists of paired ganglia connected by lateral nerves to a double connected by lateral nerves to a double ventral nerve cord.ventral nerve cord.

Nereis, an aquatic form, is dioecious,Nereis, an aquatic form, is dioecious,

but earthworms and leeches are but earthworms and leeches are monoecious.monoecious.

Reproduction is sexual.Reproduction is sexual.

REPRODUCTIONREPRODUCTION

NEREISNEREIS

PHERETIMAPHERETIMA (EARTHWORM)(EARTHWORM)

HIRUDINARIAHIRUDINARIA (BLOOD SUCKING LEECH) (BLOOD SUCKING LEECH)