Answer: The osculum.
- A The ostium
- B The osculum
- C The blastopore
- D The nephridiopore
Correct answer: B. The osculum
Explanation: Water enters through many tiny ostia and exits through the single large osculum at the top of the sponge.
Moving across the animal phyla, body organisation becomes progressively more complex: from no symmetry and cellular organisation (Porifera) through radial/diploblastic (Cnidaria), bilateral/acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), to a true coelom with full organ systems (Annelida and beyond).
Concept context
Phylum-level classification of the animal kingdom from Porifera to Chordata, based on body symmetry, coelom, and segmentation. One of the most example-heavy chapters for NEET.