What is the main difference between colonial and multicellular forms?

What is the main difference between colonial and multicellular forms? Why are colonial organisms such as volvox considered transient from unicellular to multicellular organisms?

Unlike multicellular organisms, colonial forms consist of weakly differentiated and relatively independent cells. Separate cells, rather than the entire colony as a whole, often react to individual stimuli in such organisms. Unlike the cells of most multicellular organisms, the cells extracted from the colonies do not die, but proceed to active division, forming new colonies.
Volvox is a colonial organism, which is characterized by the specialization of cells. Most cells in the colony are vegetative. Thanks to these cells, colony movement, photosynthesis, etc. are carried out. Between the vegetative cells, larger generative cells are scattered, ensuring the proliferation of volvox. The cells of the colony are not isolated from each other, but are connected by cytoplasmic bridges, which allows them to coordinate their reactions, in particular, to carry out the coordinated work of flagella. The presence of specialized cells and their coordinated functioning allows us to consider colonial organisms such as volvox as transitional forms from unicellular to multicellular organisms.

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