Perhaps you think about animals, which have appeared only once, i.e. multicellular living beings capable of complex movements.

There are a lot of other kinds of multicellular living beings, which have achieved multicellularity independently, plants and fungi being the most obvious on dry land, but most of these other multicellular life forms had to lose mobility when becoming multicellular.

Only a few have retained some limited mobility when multicellular, e.g. the slime molds, but they are much simpler than those which have lost completely mobility, by having rigid cellular walls, like plants, fungi and several distinct kinds of marine algae.

There are even several kinds of (very simple) multicellular bacteria, among Cyanobacteria (blue-green algae), Myxobacteria (resembling slime molds) and Actinobacteria a.k.a. Actinomycetes (resembling fungi).