On this side of the Atlantic, the British spy import with Patrick McGoohan was called SECRET AGENT and had a vocal theme by Johnny Rivers. The original theme tune from DANGER MAN was by Edwin Astley and called HIGH WIRE.
This summer 1966 Japanese Lost In Space magazine has an unusual monster chomping on the Chariot. I don't recall ever seeing anything like this on the series.
Could it have been inspired by the January 1966 cover of SPACE FAMILY ROBINSON?