I would say your seedlings have failed and you have weeds growing in the pot. With all the moss on the pot it has possibly been too wet and the seeds rotted.

As Mg. The big one is willowherb, not sure about the bottom one but may be the fruiting head of liverwort?

Hi, welcome to GoY, I agree, but would like to know 1 thing, is this the normal depth of soil you put in trays to sow your seeds in ?, if so, may I suggest hat next time you sow seed, you fill the tray with compost, to within about half an inch of the top, sow the seed, and lightly cover with sieved compost, { if you're using seed that needs to be covered} and water from underneath, so that as your seeds germinate, they're not goingto get 'leggy' as they search for light, and have something to put their roots into, before pricking out, Derek.

As your interest is in soil seed banks I would leave the tiny ones longer, and also wait to see if anything else emerges. (And next time follow Derek's advice...)
As you will have to have used ordinary soil rather than compost it will be more difficult than usual to keep it from compacting - it might be useful to make the top layer more sandy another time. Nothing much will germinate if the soil is hard. And you might consider siting a tray outside rather than in a lab?

Do you keep the tray covered until things start to grow? If this is a soil seed bank exercise, don't you run the risk of contamination from airborne seeds. Just asking.

Hi, thanks for all your comments! :)

I should mention, this is for a dissertation. The soil sample was taken from a dune slack area in Northern England so the soil is naturally sandy, and I am trying to see what kind of seeds are present in the soil. I have tried to keep all my soil samples moist, according to normal procedure for seed bank studies. The soil is underlain by potting compost, to prevent dehydration. These have been in the mini-greenhouse since early June and I plan to keep growing them until leaf and flower morphology becomes more apparent.
Regarding contamination, it is a risk. I have control trays in the greenhouse filled with normal potting compost so I can see what the potentially contaminating seeds are. So far, nothing has appeared in these.

Thanks again for all your help,

Chloe :)

Sounds like an interesting dissertation Chloe - following in The footsteps of Charles Darwin!
Willowherb, notoriously, gets everywhere which is why I wondered if you had kept the trays covered.