Sentence:  But there, on the very top, is a hollow full of water, with a sandy bottom; with a <WSD>blob</WSD> of jelly stuck to the side, and some mussels. 
Meaning of the word marked with <WSD> tags:  A shapeless or amorphous mass; a vague shape or amount, especially of a liquid or semisolid substance; a clump, group or collection that lacks definite shape.