Beat
From Sonic Retro
The Beat (ビート), also known as their model number E-22 Beat, is a badnik that appears in Sonic Adventure and part of the E-Series.
It's a crab-like robot that are leaked out indefinetly from wall shutes. They crawl slowly while they don't detect an enemy, but will quickly swarm in when in line of sight and set to self-destruct when they are very close. They appear in Final Egg for Sonic.