Saturday, June 30, 2012

Class XI, BIOLOGY, "Phylum Aschelminthes (Nematoda/Round worm)"

Phylum Aschelminthes (Nematoda/Round worm)

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.

4 comments:

  1. whoah this weblog is great i really like studying your posts.

    Stay up the great work! You understand, a lot of people are looking around for this information, you could help them greatly.
    My webpage : latest transfer news soccer summer 2010

    ReplyDelete
  2. Having read this I thought it was very informative.
    I appreciate you taking the time and energy to put this informative article together.
    I once again find myself personally spending a lot of
    time both reading and leaving comments. But so what, it was still
    worthwhile!
    Feel free to surf my website ; chelsea transfer news 2011

    ReplyDelete
  3. These notes are osme but why they can't download.

    ReplyDelete