Possible Clues:

• In water, inside 21 down (3)
• Might 'e have only one foot left at last?
• Is there just a little bit at the end of what's left in the water?
• Juvenile twenty-three Ac; rhymes with sinister
• Most of what's left is amphibious
• After half a century abandoned in the water
• Swimmer with feeble legs needs some beef tea
• It's not right to have had fifty cut off the top of it
• One foot in the water under the East
• Small creature that undergoes metamorphosis