I have a caseless Oase aquamax 5500lph pump in my wildlife pond, to the inlet I attached two 6" square well stamped aquatic plant pots. By well stamped I mean there is very little flashing over the holes that should be present in the pot. The pots are cable tied together, top to top, to form a box. The outlet to the pump goes through the bottom of one of the pots and in my case a hose connects the screen to the pump inlet. Such a screen takes up less space than the original pump case and I have had no problems with 'large' animals becoming stuck on it.
I have a similar set up on the side drain of a plant pond, there is a lot of blanket weed in that pond so I have to clear the screen daily and some frog tadpoles are being sucked through especially when the BW covers most of the holes. The odd snail has also been sucked out of its shell but the 'important creatures have not been sucked through.
If you are UK based the pots are those used in the B&Q aquatic plant packs. It might be worth buying 2 say flowering rush packs just to get the pots.