Thank you.
I was so exasperated by salvaging the 'invisible' OBJ and lighting the set, I did not notice the water feature also had an alpha-channel to apply...
Rendo's HBORRE kindly mentioned there's a Cycles facility for pulling Alpha channels out of RGB+Alpha textures, eg PNG
Some hapless hunting later, I've found it deep, deeep in my P_11.3...
I'd simply missed it...
D'uh...
For the benefit of any-one else who's got lost thus in Cycles' maze of twisty little passages too-much alike:
In Material room (Advanced), right-click into open area to right of PoserSurface. Follow New Node, Cycles, Texture, left-click ImageTexture
Change Projection from Box to Flat. Click on Image field to browse to relevant RGB+Alpha Texture. Connect Color to Diffuse Color. Also, optionally, to Translucence_Color. Connect Alpha to Transparency. Also, optionally, to Bump. Dial to taste, render...
Take migraine meds...
Yes, a 'Gelatinous Blob', using an outer box with 'RachealMarie_in-the-flesh-seamless-tiles_74649' set's 'Flesh1 semi-transparent', which has an Alpha channel...
https://www.Renderosity.com/freestu...-seamless-tiles