Answer:
(a) The animals with bilateral symmetry are put in group
bilateria. The body can be divided into two identical right and left halves in
only one plane, e.g., platyhelminthes, annelids, arthropods, etc.
(b) Coelom is the body cavity present between the body wall
and the gut wall. Presence or absence of coelom is very important basis of
classification.
(i) Acoeiornate Coeiom is absent, e.g...
poriferous, coelentrates, ctenophores and flatworms.
(ii) Pseudocoelornate The body cavity is not lined
by mesoderm instead it is present as scattered pouches in between mesoderm and
endoderm. e.g., round worms.
(iii) Eucoelomate Presence of true coelom. True
coelom is of two types Schizocoelom Develops by splitting up of mesoderm.
(iii) Enterocoelom The mesoderm arises from wall of
embryonic gut.
(c) Germ layers gives rise to all the tissues/organs of
the fully formed individuals. On the basis of number of germ layers animals can
be
(i) Diplobiastic The body cells are arranged in two
layers on outer ectoderm and on inner endoderm, e. g.. Coelentrates,
(ii )Tripioblastic Body wail of animals is made up
of three germ layers i.e., ectoderm, mesoderm and endoderm e.g.,
Piatyhelminthes to chordates.
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