From the Super Mario Wiki
Spiny Hermits are enemies appearing in the game Super Mario Galaxy 2. They resemble purple crustaceans or mollusks with a giant white cone-shaped shell adorned with orange spikes. They first appear as uncommon enemies in the Starshine Beach Galaxy's underwater portion. They later appear as one of the main obstacles in Boo Moon Galaxy's "Haunting the Howling Tower" mission. They serve more of an obstacle rather than an enemy. Spiny Hermits cannot be defeated.
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