Could a world be dominated by white seas?

Adapting white would mean they're reflecting visible light spectra. O-type stars emit tremendous amounts of ultraviolet. Sunscreen (which can contain zinc, making them white) is often transparent. My eye glasses block UV, and they're transparent, too. So, the "intense radiation" isn't what's causing the critters to be white. On the other hand, what UV radiation does to skin here on Earth is cause it to produce melanin, turning the skin tan. What this does (among other things) is make the skin opaque to the UV light, reducing the damage it can cause.

However, O-type stars are also very bright and tend to be blue. Let's chase that for a moment. Plants are green because they reflect the blue and green spectra, absorbing instead the red spectra that's more efficient for photosynthesis. But in this case, the plants need to absorb the green and blue spectra because it's mostly what's available (this isn't quite true, but it's true enough for government work). The consequence would be black plants in that they're absorbing everything they can for photosynthesis.

So, in humans the skin darkens in the process of becoming more opaque to block light and in plants they'd turn (IMO) black to absorb as much of the spectra as possible for photosynthesis.

I know your planet doesn't have plant life, but I needed to make the point. On your planet, what we have is the primoridal ooze that's just beginning to create complex life forms. Now that I think about it, you likely do have plants on the surface already. But what would turn them white?

That's actually a problem. Energy needs to come from somewhere or life doesn't find a way. All life begins with the sun, and that means absorbing energy, and that means reflecting nothing or very little.

But let's run for suspension-of-disbelief rather than science-based. What if we assume the creatures in your ooze (not the plants, you're kinda stuck with the plants) developed a skin that needed to act in the opposite way to how skin reacts here on Earth? Rather than blocking or reflecting spectra, we want to absorb it — but not like plants.

What if your creatures developed an epidermal skin layer that worked a bit like glucose-generating solar panels. What you really want is a mirrored surface (aka "white") under the transparent skin so that the skin simply gets baked by that glorious and short-lived star! Now we're cookin' with gas! The star may be hotter than Heather Locklear back in the 80's but your planet is cold! (Oh, all right... lukewarm.) And what this mirrored (white) dermal layer is doing is injecting heat into the body by warming the epidermis and allowing the blood to take the heat inside.

So, lukewarm planet, but critters still need to be warm — especially if the early life forms are cold-blooded!

• Transparent epidermis.
• White dermis.
• Thread-thin blood vessels (so the overall view is white, not pink).

But your plants are still black or very dark red. Sorry.