I think it is called a blob (in French, we also say "patatoïde", ie. something is the shape of a potato...).
I can think of several ways to do this, but using Toxiclibs might be a good, simple one. For example, look at the toxiclibs show reel, there is one part with jittering splitting circles which is close, and I also recall a Nokia demo sporting amoeba-like creatures.

It might also be metaball-ish - check out this vid clip or search "processing metaball" -- a metalball can give you the outline while providing simple manipulation of shape via the centers.'

If you added some frame-buffer history to it (metaball-field "trails") that might hit it exactly.

kb, http://www.riftgame.com/