Eukaryotes have evolved towards one of two extremes along a spectrum of strategies for remodelling the nuclear envelope during cell division: disassembling the nuclear envelope in an open mitosis or constructing an intranuclear spindle in a closed mitosis^(1,2). Both classes of mitotic remodelling involve key differences in the core division machinery but the evolutionary reasons for adopting a specific mechanism are unclear. Here we use an integrated comparative genomics and …