I think it's like a giant tapeworm..thing. >_> Meaning the things inside of Leviathan.
It's my favorite enemy, actually. Super-dante DT against it and you can kill it in like..10 seconds. =D You get 1000 Red Orbs for it, too.
Favorite boss? I'd have to say the final fight against Arkham while using the sniper rifle and Ebony and Ivory. If you dodge alot, you can get SSStylish with ease - shoot the sniper rifle at one of those demonic dolphin looking things, and if it's leveled up enough, you can kill like six of them with one shot. =D
Gives you a hella boost for your ranking.