Dolphins' half brains are constantly awake; they switch sides of the brain for total relaxation. Interestingly, newborn dolphins do not sleep for the first month after birth.
Orcas are another species whose babies go for months without sleeping. Other Orcas are capable of napping while swimming.
Some flies sleep for 10 hours a day, while others do not sleep at all or survive on only four minutes of sleep every day.
Alpine swifts are known to fly continuously for around six months. However, scientists are unsure if they have special way of resting.
Bullfrogs are always alert and react to stimuli as though they are awake, even when they appear to be sleeping.
Most wild fish stops sleeping, when they are on journey. Even when bluefish appear to be asleep, they are constantly swimming and responding to stimuli.
Technically jellyfish have no brains to sleep, but they still take rest by decreasing their activity and have slower responsiveness to stimuli.
Insects like butterflies don't sleep; they enter torpor, a state of relaxation with a lower body temperature and slower heartbeat, resembling sleep.
Walruses may be associated with laziness and sleepiness, but these enormous animals can easily stay up for 84 hours at a stretch.