Tried to print the original on my Ender 3 Pro. Watched it wobble and noticed that it only had a little circle of brim, smaller than a quarter. Wouldn't stay in place. Found out it was only touching the baseplate by a very small area on one side. Reoriented it so that it was touching all across the bottom opening. Lost about a millimeter of detail on the bottom but was able to print it. Noted the source file had a wall that was about 1/4" thick, so went back and made it thinner since there was no advantage to the thicker shell for an FDM printer.
Use the 1.5mm shell if you intend to print at this size or larger. I read that sea urchins are typically 1 to 4 inches. A Red Sea urchin can get up to 7 inches but that looks strange to those used to only the smaller sizes.
Use the 2mm shell if you intend to print smaller than this else the shell gets too thin as the model is shrunk.

Creality

Ender 3 Pro

No

No

.25mm and "super quality

15% gyroid

Downloaded into Tinkercad. Flipped it 90 degrees on its side. Puled out a hole cube and made it bigger than the shell. Nudged the shell closer to the hole until I could see that it was touching on one side. Went to the overhead view and moved it one degree so that it was touching the vertical surface more evenly, all around the hole in the bottom. Merged them. Then flipped it 90 degrees back to the original position and centered on the build plate. Then copied it and shrunk the copy and knocked off 4mm in all dimensions. Then made the copy a hole, centered it in all directions and merged it with the original.