Which one of the following categories of animals, is correctly described with no single exception in it?
- All reptiles possess scales, have a three chambered heart and are cold blooded (poikilothermal).
- All bony fishes have four pairs of gills and an operculum on each side.
- All sponges are marine and have collared cells.
- All mammals are viviparous and possess diaphragm for breathing.
Answer
(2) All bony fishes have four pairs of gills and an operculum on each side.
Solution
(1) Crocodiles (reptiles) have a four chambered heart. ⇒ Exception exists.
(2) As per NCERT, bony fishes (Osteichthyes) have four pairs of gills covered by an operculum on each side. ⇒ No exception.
(3) Sponges are mostly marine, but some (e.g. Spongilla) are fresh water. ⇒ Exception exists.
(4) Monotremes like Ornithorhynchus are oviparous mammals. ⇒ Exception exists.
Answer: (2)