The Detested Radishark, by Jack Prelutsky:
In the middle of the ocean, In the deep deep dark, Dwells a monstrous apparition, The detested RADISHARK. It's an underwater nightmare That you hope you never meet, For it eats what it wants, And it always wants to eat.
Its appalling, bulbous body Is astonishingly red, And its fangs are sharp and gleaming In its huge and horrid head, And the only thought it harbors In its small but frightful mind, Is to catch you and to bite you On your belly and behind.
It is ruthless, it is brutal, It swims swiftly, it swims far, So it's guaranteed to find you Almost anywhere you are. If the RADISHARK is near you, Pray the beast is fast asleep In the middle of the ocean In the dark dark deep.