These types inhabit in odd-shaped shells, making them invulnerable to Isaac's attacks. While they're in their shells, they spew bullet-shots in Monstro-style if shot at. Few moments later, its head will reveal and becomes vulnerable to attacks.
- In real-life, a cod worm (actually known as "lernaeocera branchialis") is a parasitic worm of marine fish from North Atlantic.
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