Endogenous tagging of multiple cellular components in the sea anemone
 Nematostella vectensis


 The cnidarian
 Nematostella vectensis
 has developed into a powerful model system to study the mechanisms underlying animal development, regeneration, and evolution. However, despite the significant progress in the molecular and genetic approaches in this sea anemone, endogenous protein tagging is still challenging. Here, we report a robust method for knock in for
 Nematostella
 using CRISPR/Cas9. As an outcome, we generate endogenously tagged proteins that label core molecular components of several cellular apparatus, including the nuclear envelope, cytoskeleton, cell adhesion, endoplasmic reticulum, cell trafficking, and extracellular matrix. Using live imaging, we monitor the dynamics of vesicular trafficking and endoplasmic reticulum in embryos, as well as cell contractility during the peristaltic wave of a primary polyp. This advancement in gene editing expands the molecular tool kit of
 Nematostella
 and enables experimental avenues to interrogate the cell biology of cnidarians.
