❖ The body is circular in cross-section, hence, the name roundworms/nematodes.

❖ Free living, aquatic and terrestrial or parasitic.

Phylum aschelminthes/nemathelminthes(Neema=thread,helmins=worm)

❖ Organ-system level of body organization.

❖ Bilaterally symmetrical, triploblastic and pseudocoelomate animals.

❖ Alimentary canal is complete with a mouth, a well developed muscular pharynx, intestine and anus

• Mouth is armed with teeth to cut and pierce tissues

• Muscular pharynx allows the parasitic nematodes to suck blood from host body.

❖ Excretory materials are removed from the body through an excretory tube.

❖ Sexes are separate (dioecious).

Examples:

Ascaris lumbricoids (Round Worm)

Wuchereria bancrofti (Filarial worm)

Ancylostoma duodenale(Hookworm).

❖ Sexual dimorphism is present- male and female are distinct.

Females are longer than males.

❖ Fertilization internal and development direct (the young ones resemble the adult) or indirect

Wuchereria bancrofti (Filarial worm)

Ancylostoma duodenale(Hookworm)

Ascaris lumbricoids (Round Worm)

❖ Includes segmented worms

❖ Form the first group to show the true body segmentation

Phylum Annelida Annulus =little ring

❖ Body is usually worm like and divided into similar ring like segments/metameres-hence the name

Annelida and the phenomenon is called metamerism.

❖ Aquatic Annelids like Neries posses lateral appendages

called parapodia which helps in swimming.

❖ A closed circulatory system is present.

❖ Segmentally arranged paired nephridia helps in

osmoregulation and excretion.

❖ Aquatic (marine and fresh water) or terrestrial; free-living, or parasitic.

❖ Organ-system level of organisation ,bilateral symmetry, Triploblastic, and coelomate

animals.

❖ Posses longitudinal and circular muscles which help in locomotion.

❖ Neural system consists of paired cerebral ganglia (brain) which is connected to the

double ventral nerve cord by lateral nerves.

❖ Nereis, an aquatic form, is dioecious, but

earthworms & leeches are monoecious.

❖ Reproduction is sexual.

❖ Development is indirect.

Examples:

Nereis vexillosa (calm worms)

Pheretima posthuma (Earthworm)

Hirudinaria granulosa (Blood sucking leech)

Aphrodite (sea mouse)

Polygordius

Aphrodite (sea mouse) Hirudinaria granulosa (Blood sucking leech)

Nereis vexillosa (calm worms)

Spirobranchus giganteus(Christmas Tree Worm) Pheretima posthuma (Earthworm)

Polygordius

RECAP

Phylum aschelminthes/nemathelminthes❖ The body is circular in cross-section, hence, the name roundworms/nematodes. ❖ Excretory materials are removed from the body through an excretory tube.❖ Sexual dimorphism is present- male and female are distinct.Phylum Annelida ❖ Includes segmented worms❖ Form the first group to show the true body segmentation❖ Body is usually worm like and divided into similar ring like segments/metameres.❖ Posses longitudinal and circular muscles which help in locomotion.❖ Aquatic Annelids like Neries posses lateral appendages called parapodia which

helps in swimming.❖ Segmentally arranged paired nephridia helps in osmoregulation and excretion. ❖ Neural system consists of paired cerebral ganglia (brain) which is connected to

the double ventral nerve cord by lateral nerves.