why did you pull them out of the medium? why didn't you just leave them for a few more days?
after germinating are you careful when moving them into the medium.. NOT touching or knocking the tap root as this can damage and stunt it..
from seed to seedling is the first and easiest step of this process.. maybe do some more reading..
pulling a seedling out of its medium at day 8 is slightly disruptive... to say the least...
maybe someone else has an idea... but without knowing PRECISELY what you are doing every step of the way its tough to say what you doing wrong.. everything you've said so far sounds normal...
I pulled them out to photo them to show you the (lack of) development, then binned them. I've left some in for longer than this before and I've found that they just don't develop beyond this stage, they never develop proper leaves, as they've got no roots I guess.
For germinating I just put the seeds in between a few layers of wet kitchen towel in a small dish covered with cling film then put it in the airing cupboard under some towels so it's dark and warm. I wash the dish out with boiling water before use to ensure it's sterile. I always anti-bac my hands before touching anything. The seeds pop in 24 to 48 hrs and I've been potting them up as soon as the root shows, some times just a couple of mm some times longer like 1cm. I wash the pots before use and rinse with plenty of clean water. I keep the bags of moss peat, vermiculite and perlite sealed so no beasties get in. I've been putting the seeds about 1cm down in the medium, covering them over, watering them in then waiting. Some just make it to the surface in 6 to 7 days, some never make it. Those that do make it never develop proper leaves. All of them just have a short stem and no proper roots like it the photo, then I give up and bin them.
From reading journals and stuff on here I thought they usually break the surface two or three days after potting and have one or two sets of leaves a week later, at that time mine are like in the photo - something seriously wrong?