What is "nematosome"

Nematosomes are multicellular motile bodies found in the gastrovascular cavity of the model sea anemone Nematostella vectensis starlet sea anemone. First described by Stephenson in 1935, nematosomes are the defining apomorphy ( synapomorphy) of the genus Nematostella but have received relatively little study. Nematosomes can be observed circulating through the body cavity and tentacle lumen of adult anemones, occasionally coming to rest on the gastrodermis. Nematosomes that are dislodged from rest return to circulation. The lifespan of a single nematosome has not been studied.