Bloggling

From Wikitroid, the Metroid wiki

A Bloggling is an infantile Blogg, and has not yet developed its three maws and sonic blast ability. They are still aggressive, however, using ram attacks to bring down and eat foes.

While Blogglings don't have a set weak point, attacking them may or may not harm them; simply put, you could shoot one of them in one spot and kill it outright, but shoot another in the SAME EXACT SPOT and not do any damage.

In most areas where Bloggs appear after you kill all of them when you come back later there will be only blogglings. This rule is not universal there will still be Bloggs in some areas. They appear only in Metroid Prime 2: Echoes.