I learnt about
Volvox in high school biology (many years ago) and how it was a transition between a single cell organism and a multicellular single organism.
I wouldn't say its accurate to call Volvox transitional
as such, but an example of how single cells can exist
as singly or as part of an advantageous unit.. Filamentous
algae do the same in an even simpler way
There are many other algae that can live as single cells or
as a part of a colony.
FTM giant kelp is also algae.
You may recall also from intro to biol. that sponges
are colonies of cooperating cells that can also exist as
individuals. Hydra are slightly more complex.
Living organisms such as these are not necessarily the
same as the earliest multicellular organisms, but show that
the move from single cell to multi is not the huge step
that the lower rungs of creationists imagine.
Beyond the first level of multicellularity are organisms
that well exemplify how it is a step by step process.
Readily available info for all but the most adamantly
ignorent.
Creationists also think the origin of sexual reproduction is a big mystery
all the while unaware that single cell organisms also engage
in DNA exchange- again, basic biology but those who drop
out by 7th grade and have been militantly ignorant ever since
won't have heard of it.
If there is a God he might be miffed at those who so crudely
disregard and deny his works, but perhaps pity would be
more apt.