A Flap About Mantles

[Level_Head]

In this case, I need to check/learn something. I've watched octopus dissections, seen many diagrams, read many papers, and tried to observe carefully in countless photos and videos, but am not able to resolve this satisfactorily.

How is a (typical) octopus mantle structured around the water intake and exit?

Is it a single opening through which the funnel protrudes, or does the funnel structure divide the opening into two discrete intakes?

I see octopuses protruding the funnel through one side or the other, and the flaps seeming to mold around the funnel to form a reasonable seal. How flexible are the flaps that close off the mantle opening?

What keeps the flap from pushing through (i.e. "blowing out") when the octopus contracts the mantle violently, as when jetting to escape? Are the flaps restrained by tendons in the manner of heart valves?

How is the internal cavity separated into the intake side and the area feeding into the funnel? Are the gills in this separation so that water must pass through the gills to get to the funnel chamber? If so, does a large contraction, such as jetting, bypass this or is the water forced violently through the gills?

It seems form diagrams like one large undivided chamber. If that's true, what does the internal funnel opening look like in an intact animal?

 

[CaptFish]

At two minutes in this video, you get a pretty good shot of the opening and valve working.

It seems to me like it works just as our Mitral valve. at least it looks just like it.

 

[Level_Head]

Excellent video, and it's the sort of thing that I'd guessed at with regard to the flap--the mitral valve, which has restraining attachments behind it to prevent it from overextending into "prolapse":
http://brighamandwomens.org/womenshealth/hearthealth/multimedia/mitral-valve-prolapse.htm

But I don't have a clear understanding of the octopus (or squid) version of this valve -- not even enough to know for sure if there is one large U shaped flap wrapping around, or a divided pair at the sides.