From Halopedia, the Halo wiki
Paelosurs are an enigmatic sightless species of cetacean found in the oceans of Beta Gabriel and Alluvion, where they were seeded following the firing of the Halo Array.  The paelosurs of Beta Gabriel use an incredibly evolved sense of echolocation to find their primary source of food, massive colony-swarms of krill-like organisms found in the planet's oceans. As cetaceans, paelosurs are air-breathers, inhaling and exhaling through thousands of pores scattered across the surface of their bodies.
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