Creating 'Shark Gills' Transition Shape (with Fillet?)

Hi all,

I’ve managed to do this shape but just know that there will be a better way of doing it more accurately/cleanly and with 4-sided topo idally. If possible please put the matter of isocurve density to one side as I know it’s not great - I a just looking for a way of doing this which is cleaner and can maybe respond to design changes quicker. Before I did it by creating the shapes flat and then flowing them, but couldn’t easily control the curvature so that is was always positive/converging (no hills in the middle). There’s a problem here too with the flat pieces bending back in on themselves bit - so finding it difficult to control the shapes so they have a bit of draft/are normal to the main surfaces

So far I’ve used a dummy surface to get a consistent distance for the ‘deepest point’ (0.75mm), split this dummy in the middle, and then blended from top and bottom to the middle (tangency is enough here)

Additionally, I’m wondering how I could perhaps round the edges off just a little bit… although I know there isn’t much room for anything at the moment.

Shark-Gills-form.3dm (993.0 KB)

Just make a degree 5 G1 or G2 continuous rectangular surface, then insert (symmetrically) 1 or two additional isocurves off the edges to obtain some more CPs, then scale them (symmetrically) down so as to arrive at the desired depth. No fillets and other painful modeling needed. I fudged this image on my smartphone, but hopefully you get the idea.