Myxomycetes are more commonly known to mushroom enthusiasts as Slime Moulds.
Slime moulds are usually very tiny, with lots being invisible to the naked eye, and those that can be seen are easily missed. They are a primitive group of fungi which usually live on dead or rotting wood and their purpose is to help with the decomposing of dead vegetation. There are many different species perhaps into the hundreds and this is a Subject in itself. Some fungi books include a few examples of the more visible and common types that enthusiasts might encounter.
The photograph below shows Ceratiomyxa fructiculosa. This was found at Elvaston Castle Country Park, Derbyshire during October 2015. A very tiny structure consisting of minute, off-white club-shaped bodies (0.5 mm to 1 cm tall) that can look almost translucent, or pale grey. It was growing in small lines on a dead branch lying on the ground.