Phylum Aschelminthes (Nematoda)

• The body of worms of aschelminthes in cross-section is circular, hence the name round worms.
• Habitat - They may be free-living, aquatic and terrestrial or parasitic in plants and animals.
• Level of organization - Round worms have organ-system level of organization.
• Body symmetry - They are bilaterally symmetrical.
• Body wall - They are triploblastic animals.
• Coelomic cavity - They are pseudocoelomate animals.
• Digestive system - This is the first phylum to have a complete digestive system, with a well developed muscular pharynx.
• Excretory system - An excretory tube removes body wastes from the body cavity through the excretory pore.
• They are dioecious - the sexes are separate i.e., males and females are distinct. Often females are longer than the males.
• Fertilization is internal.
• Development may be direct - the young ones resemble the adult, or indirect.
• Examples: Ascaris (round worm), Wuchereria (filaria worm), Ancylostoma (hookworm).
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