It is a mistake to believe that humankind's collective unconscious, the symbols that we all share, is uniform and detailed enough to permit a dictionary of meanings of all objects and actors in dreams.

Perhaps a few things like Mother, Father, Phallic symbol will have much the same resonance for most of us, but I don't think that it goes much further than that.

It is impossible to say with any degree of veracity that, for instance, a Crab always means separation in a dream, or even that it usually means that. To say this would be to say that differences in culture and individual temperament, milieu and personal history are all trivial and irrelevant.

the only way to find out what the thing, person, action or circumstance means is to ask the dreamer what it means for them. At some level, they do know, and they can often vocalise this knowledge if asked the right question.

Start by asking questions like:
What does the crab mean to you?
Why is it there?
Does it want to be there?
What does it want?
How does it feel about you?
How does it feel? Is it happy?
How do you feel about it?
What did you expect it to do?
Why did it do what it does?

It is not the thing in itself, but the emotional weight, the motivation and relation to the dreamer that is important.

Finally, do not interpret a dream is if it was a jigsaw puzzle, a list of pieces that must all be put together and is then complete, solved, finished.

Dreams are like water. A dream is like a well. You can bring many buckets of meaning up from the depths, but the dream remains, deep and quiet, mysterious and fluid.