Real organs are absent in
(a) Mollusca
(b) Coelenterata
(c) Arthropoda
(d) Echinodermata

Correct Answer: (b) Coelenterata

Explanation:

 Coelenterates are radially symmetrical and motile organisms, that either live in colonies or as solitary organisms.

These organisms have a coelenteron, a body cavity with only one opening. They don't have real organs.