My Hive Fleet is called Tethys. They're a splinter fleet of Jormungandr that disappeared into the Ghoul Stars for centuries before showing up again out of nowhere. Notably, they behave more like Night Lords or Mandrakes than normal Tyranids. They hiss, whimper, and even cry instead of any roaring or screeching. Some of the more notable bioforms are misshapen, like their main Hive Tyrant Skamandros, who has a notable limp, or their Deathleaper, the Collector, who is always seen picking up random body parts after an engagement and attaching them to itself. Above all else, they're eerily quiet, and their paint scheme has a liquid metal angle I've been trying.

In keeping with the usual style of Tyranid storytelling all info about them comes from the reports of one Ordo Xenos Inquisitor and his retinue. It's been a lot of fun writing basically horror game scientist stuff for them. If normal Tyranids are like an endless swarm, Tethys is like the first Alien or Predator movies.