the pharoahs are about...hm...the largest might have (rough estimate) a mantle length of 40 cm? the officinalis are significantly smaller... about half that size or less.
as I fed the metasepia tonight, I had the joy of seeing it hunt for the first time! it snagged a small shrimp and for a long time afterwards, dark lines were moving down and up its mantle, terminating in the middle. It was a color show the likes of which I've never seen in any of the other species.
sadly, i wasn't expecting it, so i didn't have my camera handy to catch it on video. Another time, perhaps...