Membranipora, a flat colony of ectoprocts (they used to be called moss animalcules, or Bryozoa). They grow on leaves of brown algae and other surfaces. You often see them on mussel shells.

The free-swimming cyphonautes larva of this organism can be found in the Centre of Larval Development.

 
Part of the Collection of the Other Invertebrates of the Micropolitan Museum © Wim van Egmond