Could the ocean hide intelligent life we would not recognize?

Yes — the ocean could hide intelligent life we wouldn’t recognize at first.

Why:

• Different nervous systems: Intelligence might be distributed, not centered in one brain like ours. Octopus-like biology is one example; a stranger form could look even less familiar.
• Unfamiliar signals: It could communicate with chemicals, light patterns, vibrations, pressure changes, or bioelectric cues that humans would miss.
• No human-style technology: Underwater life wouldn’t have fire, and many land-based technologies wouldn’t develop the same way, so intelligence might show up as behavior or ecology instead.
• Slow deep-sea pace: Cold, dark, low-energy environments can make life seem passive even if it is highly capable.

So the safest answer is: yes, it’s plausible that the ocean contains intelligent life we’d overlook because it doesn’t look like our idea of intelligence.