Bioniac

Phylum – Annelida • Latin , annulus : little ring • 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 .  • T riploblastic , metamerically segmented   • coelomate . • Their body surface is distinctly marked out into segments or metameres  , which is why the phylum name is  Annelida   •They possess longitudinal and circular muscles which help in locomotion.  • Aquatic annelids like  Nereis possess lateral appendages ,  parapodia , which help in swimming.  • Circulatory system Closed .  • 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 . • Sexual   Reproduction. Example: • Ne...