I think it is stage 2
At stage two, the skin breaks open, wears away, or forms an ulcer, which is usually tender and painful. The sore expands into deeper layers of the skin. It may appear as a scrape, blister, or a shallow crater in the skin. At times this stage looks like a blister filled with clear liquid. Also at this stage some skin may be damaged beyond repair or may die.
The chemical equations for the processes are opposite of each other
a-shellfish is your answer
The instrument of choice would be the the clam shell sampler, which is also know as a grab sampler. Another instrument they use is the piston corer which is an open tube on a cable that gets dropped from a ship.
