Matt,
Two of the diagnostics (asside from the ocellus or false eyespot) of hummelincki/filosus is an arm length of roughly 2.5 times the mantle and a arms that narrow very quickly. I have also noted the peach speckled underside and the purple rings around the edge of the suckers (trim as CaptFish calls it

) to be a common factor (they can show a completely white underside on occassion but typically it will be the peach specking). The ability to turn the "eye lid" (not sure of the proper name for this) red is also common (but may not be diagnostic as I don't know how many other species can do this). I missed a totally evil shot of Octane flashing this from very dark red to white once (without moving any other part of the body) and commented on how scary this might look to a diver. I am relatively certain this is hummelincki and, given the supplier likely from Haiti.
I have also commented on my thoughts that there are two sizes and possibily two related species that fall under this name. The larger of the two seem to have much larger mantles in terms of thickness (width) than the dwarf sized (look at
Octane and
OhToo and then at
Maya and
Serendipity). Hopefully you can see that the later two were much more delicate and lacked the girth of the first two.
As far as being active in the tank. What you are remembering is the description of senescence. Hummelincki are day active and you just put it in a new environment so any activity for the next week or two will be acclimation oriented. The behavior you don't want to see is random movement without purpose, breathing difficulties and spiral curling of the arm tips (not sure hummelincki shows the later though). However, even these symptoms in a newly introduced octopus are not necessarily signs of old age. Just accept that you have two weeks to be on pins and needles and take a couple of antacids, it will be like this for every new one you keep.
