Kemusi

Kemusi (ケムシ) is a badnik in Sonic the Hedgehog CD's Quartz Quadrant. It isn't documented in any instruction manual, but it is referred to as "kemusi" (the Japanese word for caterpillar) in the game's source code. It is a variant on Sonic the Hedgehog's Caterkiller, except that it:

• moves by compressing and expanding itself, rather than undulating
• doesn't break apart when hit on a part other than its head

Just hit on the head to destroy.