Chapter 4 – Animal Kingdom – Summary

The basic fundamental features such as level of organisation, symmetry, cell
organisation, coelom, segmentation, notochord, etc., have enabled us to broadly
classify the animal kingdom. Besides the fundamental features, there are many
other distinctive characters which are specific for each phyla or class.
Porifera includes multicellular animals which exhibit cellular level of
organisation and have characteristic flagellated choanocytes. The coelenterates
have tentacles and bear cnidoblasts. They are mostly aquatic, sessile or free-floating.
The ctenophores are marine animals with comb plates. The platyhelminths have
flat body and exhibit bilateral symmetry. The parasitic forms show distinct suckers
and hooks. Aschelminthes are pseudocoelomates and include parasitic as well as
non-parasitic roundworms.
Annelids are metamerically segmented animals with a true coelom. The
arthropods are the most abundant group of animals characterised by the presence
of jointed appendages. The molluscs have a soft body surrounded by an external
calcareous shell. The body is covered with external skeleton made of chitin. The
echinoderms possess a spiny skin. Their most distinctive feature is the presence
of water vascular system. The hemichordates are a small group of worm-like marine
animals. They have a cylindrical body with proboscis, collar and trunk.
Phylum Chordata includes animals which possess a notochord either
throughout or during early embryonic life. Other common features observed in
the chordates are the dorsal, hollow nerve cord and paired pharyngeal gill slits.
Some of the vertebrates do not possess jaws (Agnatha) whereas most of them possess
jaws (Gnathostomata). Agnatha is represented by the class, Cyclostomata. They
are the most primitive chordates and are ectoparasites on fishes. Gnathostomata
has two super classes, Pisces and Tetrapoda. Classes Chondrichthyes and
Osteichthyes bear fins for locomotion and are grouped under Pisces. The
Chondrichthyes are fishes with cartilaginous endoskeleton and are marine. Classes,
Amphibia, Reptilia, Aves and Mammalia have two pairs of limbs and are thus
grouped under Tetrapoda. The amphibians have adapted to live both on land and
water. Reptiles are characterised by the presence of dry and cornified skin. Limbs
are absent in snakes. Fishes, amphibians and reptiles are poikilothermous (coldblooded).
Aves are warm-blooded animals with feathers on their bodies and
forelimbs modified into wings for flying. Hind limbs are adapted for walking,
swimming, perching or clasping. The unique features of mammals are the presence
of mammary glands and hairs on the skin. They commonly exhibit viviparity.

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