Colobonema sericeum is a species of deep-sea hydrozoan in the family Rhopalonematidae that was first described in 1902.

[1] This semi-transparent organism is found in the mesopelagic zone, has 32 tentacles, and has a bell diameter of up 45 mm.

[2][3] They are holoplanktonic and never attach to the seafloor as part of their polyp life cycle, but instead have embryos that develop directly into a small, swimming medusae.

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