Chapter 10- Kingdom Anamalia

Phylum Aschelminthes (Nematoda/Round worm)

Nematoda are called Pin worm or round worms.

MAIN CHARACTERS

HABIT AND HABITAT

• Nematoda have a very wide distribution and they seem to have mastered almost every habitat.

• Free living nematodes are found in the sea, fresh water or in the soil in all kinds of environment.

• There are also many Parasitic nematodes found in all groups of Plants and animals.

• The Saprophagous species live in decomposing plant and animal bodies and in rotting fruits.

NATURE

They have a bilaterally symmetrical, cylindrical body, glistening smooth surface. They are triploblastic.

EXTERNAL FEATURES

• They show no trace of segmentation.

• Most of the free living nematodes are less then a millimeter length.

• Some of the parasitic species attain a length of several meters e.g. Guinea worm (Dracunculus medinensis).

• They are usually long, round, tapered at both ends showing very little morphological diversity from species to species.

• The mouth of nematodes is modified for various modes of feeding such as cutting, tearing, piercing and sucking fluids from the host.

• Body is covered by cuticle, which moults only during the period of growth.

INTERNAL FEATURES

• The organs are packed in parenchyma when young, but later on it disappears in adult. So that organs lie in a fluid filled cavity. This cavity is termed as PSEUDOCOEL and it has not peritoneum.

• Muscles are only longitudinal.

• Excretory system has no flame cells.

• Alimentary canal is straight with ectodermal fore and hind gut and an endodermal mid gut.

REPRODUCTION

• Sexes are generally separate.

• Gonades are tubular and continues with their ducts.

• Female organs are usually paired and open by vulva.

• Male organs are single and open into a cloaca.

• The life cycle of Parasitic species involves one, two or more hosts

EXAMPLES

Ascaris (Round worms), Hookworms and Thread worms etc.

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