I'm curious for anyone familiar with all this, why is it that fungal mycelium colonies and Portuguese Man-o-wars aren't considered multicellular organisms but things like slime molds are? Fruiting fungi even have specialized reproductive cells, and Portuguese Man-o-wars have two sexes, each specimen having all cells of the same sex in a single colony. What's the determining factor or set of determining factors that deliniate colonies of single cell organisms from multicellular organisms?