Amoeba proteus
As Amoeba proteus you would have no fixed shape at all. You would flow across pond sediment like a drop of living jelly, wrapping yourself around anything edible.
A body that keeps changing
Amoeba proteus is a single-celled organism, or protist, living in freshwater ponds and slow streams, usually on the bottom or among decaying plants. It is huge by cell standards: commonly 220–760 micrometres long, so big specimens are just visible to the naked eye as white specks. The species name comes from Proteus, the Greek sea god who could change form at will.
You would move by pushing out finger-like extensions called pseudopodia, ‘false feet’. Your cytoplasm streams forward into the growing tip, driven by actin and myosin – the same proteins that power human muscles – while the rear end contracts. The pace is a leisurely fraction of a millimetre per minute.
Dinner by engulfing
You eat by phagocytosis: surrounding a bacterium, alga, smaller protist or even a small ciliate with pseudopods until it is enclosed in a food vacuole, where enzymes digest it. Living in fresh water creates a constant problem, as water seeps into the cell; a contractile vacuole collects the excess and squirts it out, preventing you from swelling and bursting.
Like many protists, you have no eyes or nerves but react to light, chemicals and touch, retreating from bright light and creeping towards food.
Splitting, not dying
In good conditions an amoeba grows and then divides into two by binary fission, roughly every one to two days at room temperature. There is no corpse in this process: the parent simply becomes two offspring. Most lives end in being eaten by small animals such as worms or crustaceans, or when the pond dries up. Amoeba proteus is harmless to people; it is a different, rare free-living amoeba, Naegleria fowleri, that occasionally causes serious brain infections from warm fresh water up the nose.
