Shelbugs are slow-moving creatures native to Bryyo. They develop a Phazite shell when they reach maturity; until then, they use spines to defend themselves. Based on scans, these are most likely the larval form of the Gelbug.
Metroid Prime 3: Corruption
Attacks by firing Phazon spines. Soft body is vulnerable to attack.
Shelbugs are slow-moving roaming insects whose soft bodies are easily damaged. Until they reach maturity they will not develop their Phazite shell. Unable to retract into a shell to avoid damage, they must aggressively attack any potential threat. They will extend sharp spines to fend off attackers or propel these spines at enemies.