The sound board is a Playmatic SOUND 4. The schematic diagram is marked "MPU IV". Pictured in this listing is a board from this game clearly marked "MPU V". We have seen a picture of a Nautilus playfield (not shown here) reported to be an earlier version of this game. It does not have the upper right flipper and does not have the three star rollovers above the lower flippers. The pop bumpers caps are different and the lowest pop bumper is in a slightly different place. The flyer shown in this listing does present a 2-flipper version but, curiously, its lowest pop bumper is in a different place than the game we saw. Also, its string of inserts in the lower left playfield are arranged differently than any other playfield we have seen. We do not know if this 2-flipper version is MPU IV or MPU V. Barcelona artist Blas Gallego told us he sold artwork to a pinball company years ago for use on pinball machines. His original artwork used on the backglass for Nautilus can be seen here and his playfield art can be seen here.