A Seohl is one of my original species from the podcat universe! 
I sketched up this little study of Seohl pockets a while back when I was trying to figure out how their anatomy worked.
For now this is as close as I picture it in my head and that is good enough 

Hopefully it is clear enough to understand! They tuck their arms into the pouches located over their chest, the skin which is incredibly stretchy and rubbery is hooked onto the paw (probably by the claws) so to speak and extended to form a flipper over the arm. Similarly the back feet are tucked into the fluted tail (which has a water vent at the end) to reduce drag in the water and allow them to move much faster.
I imagine them having minor control over the slight loosening and contracting of the pockets so they can keep them somewhat sealed when not necessary. Like a small muscle contraction.

This is an anatomically correct female Seohl :3 same design as the one in the temp ref sheet. I guess shes becoming a character of mine!

 Do not use, copy, heavily reference or re-distribute this artwork in any way without my permission. The Seohl species and design is © Holly Hindle CunningFox