Largest of all Wormbrains in combined mass, the Nemateuthis houses a single mated pair of immense, aggressive roundworms, hundreds of eggs and up to a dozen hatchlings, regularly replacing one another in a steady cycle. Though soft, fragile and easily frightened, the host body is well protected by the raw strength, sharp reflexes and caustic saliva of its ravenous worms, coordinated by the collective consciousness of their minute, endoparasitic brain-flukes.
When all else fails, the Nemateuthis host may break free and escape with the remaining eggs, seeking a dark and secluded place while the new brood develops. Despite the ease with which they replenish themselves, the worms never forget the scent of an attacker who injured one of their "family."
I've had this idea to make a "squid" out of a host and its parasites for years, going through a lot of revisions in my head.
The elder worms are based on certain carnivorous nematodes, though the real world examples always have three jaws. Nematodes do have those little "swirls" on their head ends, or various other shapes that all look like little doodles in their skin. They're chemical sensors! I'll probably do a nematode article on Bogleech sometime soon-ish.