Micropalaeosoma balticus (formerly "Palaeosoma balticus" ) is an extinct, fossil turbellarian flatworm known from Baltic amber of Kaliningrad, Russia, that lived approximately 40 million years ago. It measured approximately 1.5 mm in length and is the oldest and most complete flatworm fossil yet discovered.
Micropalaeosoma balticus was an apex predator
Worms by any definition are not, and pretty much cannot be apex predators. They do not sit atop the food chain and have natural predators, and as such cannot be apex.