Hydractinia is a colonial hydrozoan that occurs on gastropod shells occupied by hermit crabs. Traits such as its small size, transparency, short generation times (1-2 months), daily spawning of hundreds of gametes, accessible embryos, and long lifespan, make it an especially tractable model organism. An international consortium of partners has undertaken the process of generating fully sequenced genomes from two Hydractinia species (H. echinata and H. symbiolongicarpus).