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Which one of the following categories of animals is correctly described with no single exception in it?
A
All mammals are viviparous and possess diaphragm for breathing
B
All reptiles possess scales, have a three chambered heart and are cold blooded (poikilothermal)
C
All bony fishes have four pairs of gills and an operculum on each side
D
All sponges are marine and have collared cells
Detailed Solution
Bony fishes (class Osteichthyes) have four pairs of gills that are covered by an operculum on each side; this holds for the class without exception.
Mammals: not all are viviparous, since the monotremes (e.g., platypus, $Ornithorhynchus$) are oviparous.
Reptiles: crocodiles have a four-chambered heart, so 'three chambered heart' has an exception.
Sponges: most are marine but some, such as $Spongilla$, live in fresh water.
Hence the category described with no exception is the bony fishes.
Mammals: not all are viviparous, since the monotremes (e.g., platypus, $Ornithorhynchus$) are oviparous.
Reptiles: crocodiles have a four-chambered heart, so 'three chambered heart' has an exception.
Sponges: most are marine but some, such as $Spongilla$, live in fresh water.
Hence the category described with no exception is the bony fishes.