Avoid it next year by starting them off in individual pots.

Wow, I'm having exactly the same problem. Even had some beans manage to germinate but though the seed was half out of the ground, it was loaded with worms. I had planted green bean seeds of the same variety but from two different seed companies. The one variety was coated with pink stuff to keep the seeds from rotting. This is the kind that was trying to come up. Some of those seeds were not affected with worms at all. The other variety was totally mush and often full of worms if I could find the seed.

The worms are very fine and threadlike and quite speedy. If you touch them they curl into a spiral. On some of the larger ones you can see two antennae. I'm wondering if they are tiny millipedes or centipedes attracted by the rotting beans? I do have some centipedes in my garden but not many. I have seen these tiny worms very occasionally in my compost pile.

What I've done was dig up the infested seeds and try to get all the worms in the surrounding soil and then replant with the treated bean seed. We have had a very cool wet spring but it is supposed to turn sunny and hot next week so I'm hoping the second planting will work.

The seeds that had germinated and were trying so hard - I couldn't bear to pull them up so doused them with insecticidal soap. This did not appear to kill the worms but did cause them to flee and I picked them off the ground. It was only 3 plants, so we'll see. Don't know what I'd do if I'd planted a long row of them.