question_answer 30)

  In which group of animals, coelom is filled with blood? (a) Arthropoda                  (b) Annelida                                       (c) Nematoda                    (d) Echinodermata

Answer:

  (a) The true coelom is a body cavity which arises as a cavity in embryonic mesoderm. In arthropods, annelids and Mollusca, it develops by splitting up of mesoderm. It is called schizocoelom. But in the cavity of Arthropoda and non-cephalopoda molluscs a colourless blood is present and is called haemocoel. In echinoderms and chordates, the mesoderm arises from the wall of embryonic gut or enter on as hollow outgrowths or enterocoelomic pouches. In coelenterates body cavity is absent. In round worms the body cavity is not lined by mesoderm, instead the mesoderm is present as scattered pouches. Such body cavity is called pseudocoelom.