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That would be Spinellus fusiger. It is a parasite that attacks other fungi. It is a fungus, itself.

It's a fungus from too much moisture. I would turn the tray around so the light is on the other side and they will straighten up. Increase the air flow even if you need to add a fan. You also can thin the seedlings since there are multiple ones growing in each cell.

Here are more tips:

https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/preventing-white-fluffy-fungus-on-seed-starting-soil.htm

https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/seedlings-after-germination.htm

Not technically, but it is close enough to be considered one. Dog Vomit Slime Molds are very beneficial to the garden, though unsightly.

Their diet consists of bacteria, and when you see them it is likely that you have a bacterial infection in the area. It should be left to clean up your soil, as the bacteria present may harm your plants.

Here is an article that will give you more information:

https://www.gardeningknowhow.com/ornamental/fungus-lichen/what-is-slime-mold-slime.htm

There are a few things you can try! This article will help:

https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm

It's a type of mushroom. To eliminate them, make your soil less hospitable. They like shady, moist areas with decaying matter such as leaves, sticks, etc. I'm surprised it thrives in your dry environment.

https://www.gardeningknowhow.com/ornamental/fungus-lichen/environmental-benefits-of-fungi.htm

https://www.gardeningknowhow.com/lawn-care/lgen/eliminate-mushrooms-in-your-lawn.htm

Unfortunately, your photos did not come through. It does sound a bit like what is known as Dog Vomit Mold. This is good news, and bad news.

The good news is that this organism eats bacteria. This is what it will consume the most of during its life cycle.

The bad news is that your soil is bacterial. Usually, this means that it stays far too moist to support plant life. This is where bacteria thrive. Fortunately, it is where the slime mold thrives, as well.

I would let the organism do what it does best- It acts as a soil cleaner. Make sure to let the soil dry out thoroughly between waterings, if possible.

If you want to speed things up, you can use a fungicide to help treat your soil. This article will help you with fungicide use:

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

This article will explain more on the subject of Slime Molds:

https://www.gardeningknowhow.com/ornamental/fungus-lichen/what-is-slime-mold-slime.htm