Define the terms and give one example of each
(a) Bilateral symmetry
(b) Coelom
(c ) Triploblastic

Explanation

(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) Acoelomate Coelom is absent. e.g., poriferous, coelentrates, ctenophores and flatworms.
(ii) Pseudocoelomate 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.
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 the number of germ layers animals can be
(i) Diploblastic The body cells are arranged in two layers on outer ectoderm and on inner endoderm, e.g., Coelentrates.
(ii) Triploblastic Body wall of animals is made up of three germ layers i.e., ectoderm, mesoderm and endoderm e.g., Platyhelminthes to chordates.