ABSTRACT: Planktonic embryos are unprotected and experience high mortalities. Risk exposure and its consequences for survival depend very much on developmental time, which, in turn, is strongly affected by temperature. Developmental times in planktonic embryos have recently been correlated with cell cycle duration and egg size. Here, we elaborate on this by deriving a developmental time model from cell proliferation dynamics in which the effect of temperature on developmental time is modelled through the effect of temperature on cell cycle duration. Published cell lineage data from Caenorhabditis elegans and on developmental times in planktonic embryos were used to assess the validity of model assumptions. Analyses demonstrate that a common parameter set accounts for 94 to 95% of observed variance in developmental times for species from the same phylum. This percentage drops considerably when species from different phyla are included in a single analysis, suggesting taxonomic differentiation in the developmental parameters of the model. The model provides a theoretical framework for anchoring observed variability in organism traits at the cellular scale, and we provide suggestions for future experimental work designed to connect developmental time in organisms to their cell proliferation dynamics.