you can't do any damage to these things when they go into what I call "Defense mode" where they suck into their shells, blm's are the only good thing for this, to nuke when they come out and wait when they stay in that mode. DoT with weapons is almost impossible on such a high level one as well.
Me (75BLM) and a 75 Bard almost killed this thing with barely any damage being done to us. The only problem though is that you have to kill it before the manaclipper ride ends. Gonna try to kill it today and get the shell.
This drops from an NM called Harajinite. I was on the mana clipper and someone fished up the NM Cyclopean (sp?) Uraganite and was fighting it. Then another person fished up this thing. It agroed the bard that fished it up and she invited me to her party so i could "tank" for her. We could do absolutly no damage, i would say that this NM is harder than the Cylcopean uraganite but i am not sure. probly level 70 + .