Hi Steve,
Great pics.
At first view does not look like Echinoteuthis to me. But let me check my notes and I will be back to you.
Nevetheless, some large "mastigoteuthid-like" squids, develop in "older stages", some kind of reticulated, cartilaginous tissue on the skin. So I think is a common feature in meso/bathypelagic squids. I have seen that in other species. If you could take a SEM photo will be a good reference for the future.
The armature remind me a grimalditeuthid, you are right, but also the "subconus" in the ventral view where the gladius extends (? clear)
is very gelatinous, uncommon in mastigoteuthids.
Well, like in pocker, I examined one very similar specimen from south of Japan and I tried to placed it into the Chiroteuthidae, but I was not convinced completely with the main taxonomic features. So I named species "Mastigoteuthis" sp F., 1993 (just to put any name). Later I decided to placed it as a link between Chiro and Mastigo families. This could be a new family, under the Chiroteuthoidea (?).
At generic level could be anything, but at family level I will put together, as I said before, Mastigo/Chiro as a single family, so it could fit in between.
Well, too much speculating, but I will check my old notes and I will bring some info on my specimen from Japan.
Great squid, Steve! Congratulations!
Alejandro