A
Group - Reptilia ; Characteristics - Crawling mode of locomotion, all are terrestrial
B
Group - Chondrichthyes ; Characteristics - Placoid scales, electric organs, claspers
C
Group - Amphibia ; Characteristics - Tympanum, two pairs of limbs
D
Group - Mammalia ; Characteristics - Mammary glands, lungs, direct development
Solution:
All mammals possess mammary glands, lungs and undergo direct development. Some reptiles are aquatic (e.g., sea snakes, turtles). Electric organs are present only in some cartilaginous fishes (e.g., Torpedo); not all. Some amphibians are limbless (e.g., Ichthyophis).
