Possible Clues:

• Semi-aquatic boa with 11 humps, writhing
• Like the creatures at 17-, 26-, 37- and 51-Across, jokingly?
• Hearing aid from exhibit at the centre is consuming Marseilles where it's of use in and out of the water
• Like the D-Day assault on Normandy
• For use on land and in water
• "How's the water, ___?"