They could be slugs but may be attracted to the plant because of stress. The lower leave often turn yellow and fall off. Is the base rotting if so its root rot. Not a whole lot you can do about that but take cuttings and try again. Slugs dont really bother Impatiens only when they are seedlings, they would prefer something else.

The seeds could fit that description too! I remember thinking how odd they were when I first saw them!